Waxy corn

ABSTRACT

The present disclosure involves the production of Waxy maize. Compositions and methods are provided for knocking out expression of the Waxy (Wx1) gene in maize by making double strand breaks at one or more target sites in an endogenous WX1 encoding sequence. Some methods employ one or more guide polynucleotides and a Cas endonuclease, wherein Cas endonuclease is guided by the one or more guide polynucleotides to recognize and introduce double strand breaks at specific target sites in and around the Wx1 gene. Also provided are compositions and methods for the production of Waxy maize plant cells, plant explants, seeds and grain.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of International Application NumberPCT/US2017/014903 filed Jan. 25, 2017, which claims the benefit of U.S.Provisional Application No. 62/287,115, filed Jan. 26, 2016, the entirecontent of which is herein incorporated by reference.

FIELD

The field is molecular biology, and more specifically, methods forediting the genome of a maize plant cell to produce Waxy corn.

Reference to Sequence Listing Submitted Electronically

The official copy of the sequence listing is submitted electronicallyvia EFS-Web as an ASCII formatted sequence listing with a file named20170116_BB2535PCT_SequenceListing_ST25.txt created on Jan. 16, 2017 andhaving a size of 35 kilobytes and is filed concurrently with thespecification. The sequence listing contained in this ASCII formatteddocument is part of the specification and is herein incorporated byreference in its entirety.

BACKGROUND

Maize kernels consist primarily of starch which is composed of two typesof polysaccharides—amylose and amylopectin. In normal dent maize, theratio between amylose and amylopectin is approximately 27% to 73%. In“Waxy” corn, however, the starch is composed exclusively of amylopectinand is a valuable commodity due to its superior properties, includingbut not limited to a higher hot viscosity; production of softer, morestable, and clearer gels; and higher freeze-thaw stability. The starchfrom Waxy maize has appreciable end uses in industrial and food-gradeproduct streams, such as, for example, as ingredients (thickeners),adhesives and bioplastics, ethanol fermentation, and possibly in silage.

The Waxy (Wx1) gene in maize encodes a granule-bound starch synthaseenzyme, NDP-glucose-starch glucosyltransferase, that is responsible forproduction of amylose in pollen and endosperm tissue. When the Waxy geneis knocked out, as in recessive (wx1) alleles, “Waxy” maize, or maizewith high amylopectin starch in its pollen and kernels, results. Thereare more than 40 mutant alleles known for the Waxy locus, and producingWaxy maize typically involves breeding a mutant allele into modern maizeinbreds for the production of industrial hybrids. However, the mutantalleles are recessive, which can make the breeding process cumbersome,requiring substantial time and resources. Moreover, the resultingproducts may have quality issues; and the trait may exhibit incompletepenetrance. Most importantly, there is often a yield penalty associatedwith introgression of the waxy trait.

There is a need to produce Waxy maize more efficiently and in a way thatwill reduce yield drag associated with introgression of Waxy mutantalleles into elite maize lines via conventional means.

SUMMARY

The methods described herein relate to the generation of maize lineswith mutations that knock out the Waxy (Wx1) gene. Compositions andmethods are provided for editing of the Wx1 gene locus in a maize plantcell.

Methods for obtaining a Waxy maize plant are presented herein in whichdouble strand breaks are introduced into one or more target sites in anendogenous WX1 encoding sequence in a maize plant cell to produce amaize plant cell with a modified Wx1 nucleotide sequence, wherein themodified Wx1 nucleotide sequence comprises a nucleic acid alterationthat knocks out Wx1 gene function. A maize plant is generated from themaize plant cell; and the maize plant produces grain with an increasedpercentage of amylopectin compared to a second maize plant comprising afunctional Wx1 gene. The method may further include introducing a Wx1polynucleotide modification template in the maize plant cell, in whichthe Wx1 polynucleotide modification template has at least one nucleicacid alteration (when compared to the endogenous WX1 encoding sequence)that knocks out Wx1 gene function when incorporated into the endogenousWX1 encoding sequence. The double strand break may be induced by aTALEN, a meganuclease, a zinc finger nuclease, a CRISPR-associatednuclease, or any other double strand inducing agent known to one ofordinary skill in the art.

In some aspects, the double strand inducing agent is a CRISPR-associatednuclease and one or more guide RNAs are provided. In these methods, oneor more guide RNAs and a Cas endonuclease are provided to a maize plantcell comprising an endogenous WX1 encoding sequence, in which each guideRNA is capable of forming a complex with Cas endonuclease that enablesthe Cas endonuclease to introduce a double strand break at a target sitein the endogenous WX1 encoding sequence in the genome of the maize plantcell. Alternatively, one or more guide RNAs are provided to a maizeplant cell comprising a Cas endonuclease and a an endogenous WX1encoding sequence, wherein each guide RNA is capable of forming acomplex with Cas endonuclease that enables the Cas endonuclease tointroduce a double strand break at a target site in the endogenous WX1encoding sequence in the genome of said maize plant cell. In eithermethod, maize plants are obtained from the maize plant cells; and themaize plants may or may not be evaluated for the presence of a nucleicacid alteration that knocks out the function of the Wx1 gene. A maizeplant that produces grain with an increased percentage of amylopectincompared to a second maize plant comprising a functional Wx1 gene isthen selected.

In some aspects, in the methods that use a CRISPR-associated nuclease,one guide RNA may be provided. The guide RNA may comprise a variabletargeting domain that is complementary to SEQ ID NO:4 [WX-TS1].

In some aspects, in the methods that use a CRISPR-associated nuclease,two guide RNAs may be provided. In one aspect, a first guide RNA maycomprise a variable targeting domain that is complementary to SEQ IDNO:1 [WX-TS4] and a second guide RNA may comprise a variable targetingdomain that is complementary to SEQ ID NO:2 [WX-TS8]. In another aspect,a first guide RNA may comprise a variable targeting domain that iscomplementary to SEQ ID NO:1 [WX-TS4] and a second guide RNA maycomprise a variable targeting domain that is complementary to SEQ IDNO:9 [WX-TS7]. In another aspect, a first guide RNA may comprise avariable targeting domain that is complementary to SEQ ID NO:1 [WX-TS4]and a second guide RNA may comprise a variable targeting domain that iscomplementary to SEQ ID NO:8 [WX-TS5]. In another aspect, a first guideRNA may comprise a variable targeting domain that is complementary toSEQ ID NO:7 [WX-TS6] and a second guide RNA may comprise a variabletargeting domain that is complementary to SEQ ID NO:2 [WX-TS8]. Inanother aspect, a first guide RNA may comprise a variable targetingdomain that is complementary to SEQ ID NO:7 [WX-TS6] and a second guideRNA may comprise a variable targeting domain that is complementary toSEQ ID NO:9 [WX-TS7]. In another aspect, a first guide RNA may comprisea variable targeting domain that is complementary to SEQ ID NO:7[WX-TS6] and a second guide RNA may comprise a variable targeting domainthat is complementary to SEQ ID NO:8 [WX-TS5]. In another aspect, afirst guide RNA may comprise a variable targeting domain that iscomplementary to SEQ ID NO:3 [WX-TS10] and a second guide RNA maycomprise a variable targeting domain that is complementary to SEQ IDNO:2 [WX-TS8]. In another aspect, a first guide RNA may comprise avariable targeting domain that is complementary to SEQ ID NO:4 [WX-TS1]and a second guide RNA may comprise a variable targeting domain that iscomplementary to SEQ ID NO: 5 [WX-TS3]. In another aspect, a first guideRNA may comprise a variable targeting domain that is complementary toSEQ ID NO:4 [WX-TS1] and a second guide RNA may comprise a variabletargeting domain that is complementary to SEQ ID NO:6 [WX-TS2].

In the methods above, the Cas endonuclease may be a Cas9 endonuclease. Agene encoding the Cas endonuclease may be optimized for maize and/oroperably linked to an SV40 nuclear targeting signal upstream of the Cascoding region.

The nucleic acid alteration in the Wx1 nucleotide sequence may begenerated in an elite inbred maize plant. In some aspects, the eliteinbred maize plant is a member of the Iowa Stiff Stalk Syntheticheterotic group, the non-Stiff Stalk heterotic group, or any otherheterotic group known to one of ordinary skill in the art.

Also provided are plants produced by the method and seeds produced bythe plants.

A guide polynucleotide molecule comprising a variable targeting domainthat is complementary to a target site in the maize Wx1 gene is alsoprovided. The guide polynucleotide may be RNA, DNA, or a combination ofRNA and DNA. The guide polynucleotide may have a variable targetingdomain that is complementary to SEQ ID NO:1; SEQ ID NO:2; SEQ ID NO:3;SEQ ID NO:4; SEQ ID NO:5; SEQ ID NO:6; SEQ ID NO:7; SEQ ID NO:8; and SEQID NO:9.

Methods of producing a Waxy maize hybrid plant are also provided inwhich an Iowa Stiff Stalk Synthetic maize inbred comprising a nucleicacid alteration that knocks out Wx1 gene function, is crossed with anon-Stiff Stalk maize inbred also comprising a nucleic acid alterationthat knocks out Wx1 gene function. The Waxy maize hybrid plant may havesimilar yield as a maize hybrid plant produced by a cross between theIowa Stiff Stalk Synthetic maize inbred and the non-Stiff Stalk maizeinbred, neither of which have a nucleic acid alteration that knocks outWx1 gene function.

BRIEF DESCRIPTION OF THE DRAWINGS AND SEQUENCE LISTING

The invention can be more fully understood from the following detaileddescription and the accompanying drawings and Sequence Listing, whichform a part of this application. The sequence descriptions and sequencelisting attached hereto comply with the rules governing nucleotide andamino acid sequence disclosures in patent applications as set forth in37 C.F.R. §§ 1.821-1.825. The sequence descriptions contain the threeletter codes for amino acids as defined in 37 C.F.R. §§ 1.821-1.825,which are incorporated herein by reference.

Drawings

FIGS. 1A and 1B show the structure of the Wx1 gene and the strategy forknocking out the function of the gene, respectively. In FIG. 1A, shadedsections indicate exons, and target site locations are indicated by theupside down triangles. In FIG. 1B, the dotted lines indicate deletedsequence.

FIGS. 2A and 2B depict screening for Wx1 whole gene deletion events. InFIG. 2A, qPCR primers used for deletion screening are indicated byarrows. Primer pair P4F/P8R was used for deletions generated using theCR4/CR8 or CR6/CR8 pairings. Primer pair P4F/P7R was used for deletionsgenerated using the CR4/CR7 pairing. Primer pair P4F/P5R was used fordeletions generated using the CR4/CR5 deletion. Primer pair P10F/P8R wasused for deletions generated using the CR10/CR8 deletion. Primer pairP1F/P2R was used for exon 7 and intron junction deletion screening. FIG.2B shows an amplification plot for CR4/CR8 deletion event screening.

FIG. 3 shows a sequence alignment of generated mutations (SEQ IDNOs:48-57) at the CR4/CR8 deletion junction. SEQ ID NO:47 is thesequence of the wild-type Wx1 gene at the CR4/CR8 junction. The twoshaded nucleotides are at the CR4/CR8 junction site; the remainingWX-TS4 target site sequence is in italics; the remaining WX-TS8 sequenceis underlined; and the open box indicates the PAM sequence of theremaining target site. Only a sampling of generated mutations at thejunction sequence is presented.

FIG. 4 shows a sequence alignment of generated mutations (SEQ ID NOs:59-67) at the CR10/CR8 deletion junction. SEQ ID NO:58 is the sequenceof the wild-type Waxy gene at the CR10/CR8 junction. The two shadednucleotides are at the CR10/CR8 junction site; the remaining WX-TS10target site sequence is in italics; the remaining WX-TS8 sequence isunderlined; and the open box indicates the PAM sequence of the remainingtarget site. Only a sampling of generated mutations at the junctionsequence is presented.

FIG. 5 shows a sequence alignment of generated mutations (SEQ IDNOs:69-76) with CR1 only or with CR1/CR3. SEQ ID NO:68 is the sequenceof the wild-type Wx1 gene in this region. The WX-TS1 target site is initalics; the WX-TS3 target sit is underlined; and arrows indicate thecleavage sites for WX-TS1 and WX-TS3. Sequences in bold are at the 3′end of exon 7 sequences. The open boxes indicate the PAM sequences.D7-Δ30 bp (SEQ ID NO:69) and the precise CR1/CR3 deletion (SEQ ID NO:75)are also shown. Only a sampling of generated mutations at the junctionsequence is presented.

FIGS. 6A and 6B show the Waxy maize phenotype in pollen and kernels,respectively. In FIG. 6A, T0 plants with the CR4/CR8 deletion werestained with iodine. Wild-type pollen having a functional Wx1 genestained darker blue, while Waxy pollen stained light red color. In FIG.6B, an ear of maize is shown that has both Waxy kernels (having a Wx1gene knockout) and normal wild-type kernels (functional Wx1 gene). Waxy(wx1) kernels stain lighter with iodine, while normal wild-type kernels(Wx1) stain darker.

SEQUENCES

SEQ ID NO:1 is the nucleotide sequence of the maize genomic target siteWX-TS4.

SEQ ID NO:2 is the nucleotide sequence of the maize genomic target siteWX-TS8.

SEQ ID NO:3 is the nucleotide sequence of the maize genomic target siteWX-TS10.

SEQ ID NO:4 is the nucleotide sequence of the maize genomic target siteWX-TS1.

SEQ ID NO:5 is the nucleotide sequence of the maize genomic target siteWX-TS3.

SEQ ID NO:6 is the nucleotide sequence of the maize genomic target siteWX-TS2.

SEQ ID NO:7 is the nucleotide sequence of the maize genomic target siteWX-TS6.

SEQ ID NO:8 is the nucleotide sequence of the maize genomic target siteWX-TS5.

SEQ ID NO:9 is the nucleotide sequence of the maize genomic target siteWX-TS7.

SEQ ID NO:10 is the nucleotide sequence of the modified Cas9 gene fromStreptococcus pyogenesM1 GAS (SF370) with the ST-L1 intron2.

SEQ ID NO:11 is the amino acid sequence of SV40 amino N-terminal.

SEQ ID NO:12 is the nucleotide sequence of the maize U6 polymerase IIIpromoter.

SEQ ID NO:13 is the nucleotide sequence of the WXY-CR4 gRNA expressioncassette comprising the maize U6 polymerase III promoter operably linkedto the nucleotide variable targeting domain that is complementary to theWXY-TS4 target sequence, followed by an RNA sequence capable ofinteracting with the double strand break inducing endonuclease.

SEQ ID NO:14 is the nucleotide sequence of the WXY-CR8 gRNA expressioncassette comprising the maize U6 polymerase III promoter operably linkedto the nucleotide variable targeting domain that is complementary to theWXY-TS8 target sequence, followed by an RNA sequence capable ofinteracting with the double strand break inducing endonuclease.

SEQ ID NO:15 is the nucleotide sequence of the WXY-CR10 gRNA expressioncassette comprising the maize U6 polymerase III promoter operably linkedto the nucleotide variable targeting domain that is complementary to theWXY-TS10 target sequence, followed by an RNA sequence capable ofinteracting with the double strand break inducing endonuclease.

SEQ ID NO:16 is the nucleotide sequence of the WXY-CR1 gRNA expressioncassette comprising the maize U6 polymerase III promoter operably linkedto the nucleotide variable targeting domain that is complementary to theWXY-TS1 target sequence, followed by an RNA sequence capable ofinteracting with the double strand break inducing endonuclease.

SEQ ID NO:17 is the nucleotide sequence of the WXY-CR3 gRNA expressioncassette comprising the maize U6 polymerase III promoter operably linkedto the nucleotide variable targeting domain that is complementary to theWXY-TS3 target sequence, followed by an RNA sequence capable ofinteracting with the double strand break inducing endonuclease.

SEQ ID NO:18 is the nucleotide sequence of the WXY-CR2 gRNA expressioncassette comprising the maize U6 polymerase III promoter operably linkedto the nucleotide variable targeting domain that is complementary to theWXY-TS2 target sequence, followed by an RNA sequence capable ofinteracting with the double strand break inducing endonuclease.

SEQ ID NO:19 is the nucleotide sequence of the WXY-CR6 gRNA expressioncassette comprising the maize U6 polymerase III promoter operably linkedto the nucleotide variable targeting domain that is complementary to theWXY-TS6 target sequence, followed by an RNA sequence capable ofinteracting with the double strand break inducing endonuclease.

SEQ ID NO:20 is the nucleotide sequence of the WXY-CR7 gRNA expressioncassette comprising the maize U6 polymerase III promoter operably linkedto the nucleotide variable targeting domain that is complementary to theWXY-TS7 target sequence, followed by an RNA sequence capable ofinteracting with the double strand break inducing endonuclease.

SEQ ID NO:21 is the nucleotide sequence of the WXY-CR5 gRNA expressioncassette comprising the maize U6 polymerase III promoter operably linkedto the nucleotide variable targeting domain that is complementary to theWXY-TS5 target sequence, followed by an RNA sequence capable ofinteracting with the double strand break inducing endonuclease.

SEQ ID NO:22 is the DNA version of the guide RNA in the WXY-CR4expression construct.

SEQ ID NO:23 is the DNA version of the guide RNA in the WXY-CR8expression construct.

SEQ ID NO:24 is the DNA version of the guide RNA in the WXY-CR10expression construct.

SEQ ID NO:25 is the DNA version of the guide RNA in the WXY-CR1expression construct.

SEQ ID NO:26 is the DNA version of the guide RNA in the WXY-CR3expression construct.

SEQ ID NO:27 is the DNA version of the guide RNA in the WXY-CR2expression construct.

SEQ ID NO:28 is the DNA version of the guide RNA in the WXY-CR6expression construct.

SEQ ID NO:29 is the DNA version of the guide RNA in the WXY-CR7 DNAexpression construct.

SEQ ID NO:30 is the DNA version of the guide RNA in the WXY-CR5expression construct.

SEQ ID NO:31 is the nucleotide sequence of the P4F forward primer.

SEQ ID NO:32 is the nucleotide sequence of the P8R reverse primer.

SEQ ID NO:33 is the nucleotide sequence of the P7R reverse primer.

SEQ ID NO:34 is the nucleotide sequence of the P5R reverse primer.

SEQ ID NO:35 is the nucleotide sequence of the CR4 probe.

SEQ ID NO:36 is the nucleotide sequence of the P10F forward primer.

SEQ ID NO:37 is the nucleotide sequence of the CR10 probe.

SEQ ID NO:38 is the nucleotide sequence of the NGS 2nd forward primer.

SEQ ID NO:39 is the nucleotide sequence of the NGS 2nd reverse primer.

SEQ ID NO:40 is the nucleotide sequence of the CR4/CR6 mipf1 forwardprimer.

SEQ ID NO:41 is the nucleotide sequence of the CR8mipr reverse primer.

SEQ ID NO:42 is the nucleotide sequence of the CR5mipr reverse primer.

SEQ ID NO:43 is the nucleotide sequence of the CR7mipr reverse primer.

SEQ ID NO:44 is the nucleotide sequence of the CR10mipf forward primer.

SEQ ID NO:45 is the nucleotide sequence of the CR1mipf forward primer.

SEQ ID NO:46 is the nucleotide sequence of the CR1mipr reverse primer.

SEQ ID NO:47 is the nucleotide sequence of the wild-type Waxy gene atthe CR4/CR8 junction.

SEQ ID NOs:48-57 are the nucleotide sequences of mutations generated atthe CR4/CR8 deletion junction.

SEQ ID NO:58 is the sequence of the wild-type Waxy gene at the CR10/CR8junction.

SEQ ID NOs: 59-67 are the nucleotide sequences of mutations generated atthe CR10/CR8 deletion junction.

SEQ ID NO:68 is the nucleotide sequence of the wild-type Waxy gene inthe region containing the TS1 and TS3 target sites.

SEQ ID NOs:69-76 are the nucleotide sequences of mutations generatedusing CR1 only or CR1/CR3. The D7-Δ30 bp deletion is represented by SEQID NO:69, and the precise CR1/CR3 deletion is represented by SEQ IDNO:75.

DETAILED DESCRIPTION

The present disclosure includes the production of maize plants thatexhibit the Waxy maize phenotype, i.e. increased amylopectin in pollenand kernels, as compared to a maize plant with a functional Waxy (Wx1)gene. Compositions and methods are provided for knocking out the Wx1gene in a maize plant cell by introducing double strand breaks (DSBs) atone or more targets sites and optionally providing a polynucleotidemodification template.

DSBs can be induced using any DSB-inducing agent available, including,but not limited to, TALENs, meganucleases, zinc finger nucleases,Cas9-gRNA systems (based on bacterial CRISPR-Cas systems), and the like.

TAL effector nucleases (TALEN) are a class of sequence-specificnucleases that can be used to make double-strand breaks at specifictarget sequences in the genome of a plant or other organism. (Miller etal. (2011) Nature Biotechnology 29:143-148).

Meganucleases, also known as homing endonucleases (HEases), are likerestriction endonucleases in that they bind and cut at a specificrecognition site; however the recognition sites for meganucleases aretypically longer, about 18 bp or more (patent application PCT/U.S. Ser.No. 12/30,061, filed on Mar. 22, 2012). Meganucleases have beenclassified into four families based on conserved sequence motifs, thefamilies are the LAGLIDADG, GIY-YIG, H-N-H, and His-Cys box families.These motifs participate in the coordination of metal ions andhydrolysis of phosphodiester bonds. HEases are notable for their longrecognition sites, and for tolerating some sequence polymorphisms intheir DNA substrates. The naming convention for meganuclease is similarto the convention for other restriction endonuclease. Meganucleases arealso characterized by prefix F-, I-, or PI- for enzymes encoded byfree-standing ORFs, introns, and inteins, respectively. One step in therecombination process involves polynucleotide cleavage at or near therecognition site. This cleaving activity can be used to produce adouble-strand break. For reviews of site-specific recombinases and theirrecognition sites, see, Sauer (1994) Curr Op Biotechnol 5:521-7; andSadowski (1993) FASEB 7:760-7. In some examples the recombinase is fromthe Integrase or Resolvase families.

Zinc finger nucleases (ZFNs) are engineered double-strand break inducingagents comprised of a zinc finger DNA binding domain and adouble-strand-break-inducing agent domain. Recognition site specificityis conferred by the zinc finger domain, which typically comprising two,three, or four zinc fingers, for example having a C2H2 structure,however other zinc finger structures are known and have been engineered.Zinc finger domains are amenable for designing polypeptides whichspecifically bind a selected polynucleotide recognition sequence. ZFNsinclude an engineered DNA-binding zinc finger domain linked to anon-specific endonuclease domain, for example nuclease domain from aType IIs endonuclease such as Fok I. Additional functionalities can befused to the zinc-finger binding domain, including transcriptionalactivator domains, transcription repressor domains, and methylases. Insome examples, dimerization of nuclease domain is required for cleavageactivity. Each zinc finger recognizes three consecutive base pairs inthe target DNA. For example, a 3 finger domain recognized a sequence of9 contiguous nucleotides, with a dimerization requirement of thenuclease, two sets of zinc finger triplets are used to bind an 18nucleotide recognition sequence.

Some methods presented herein employ one or more guide polynucleotidesand Cas endonuclease, wherein a Cas endonuclease is guided by each guidepolynucleotide to recognize a target genomic sequence in or around theWx1 gene and introduce double strand breaks in the target genomicsequence, thereby knocking out the function of the gene.

The term “Cas gene” herein refers to a gene that is generally coupled,associated or close to, or in the vicinity of flanking CRISPR loci inbacterial systems. The terms “Cas gene”, “CRISPR-associated (Cas) gene”are used interchangeably herein. The term “Cas endonuclease” hereinrefers to a protein encoded by a Cas gene. A Cas endonuclease herein,when in complex with a suitable polynucleotide component, is capable ofrecognizing, binding to, and optionally nicking or cleaving all or partof a specific DNA target sequence. A Cas endonuclease described hereincomprises one or more nuclease domains. Cas endonucleases of thedisclosure includes those having a HNH or HNH-like nuclease domainand/or a RuvC or RuvC-like nuclease domain. A Cas endonuclease of thedisclosure includes a Cas9 protein, a Cpf1 protein, a C2c1 protein, aC2c2 protein, a C2c3 protein, Cas3, Cas 5, Cas7, Cas8, Cas10, orcomplexes of these.

As used herein, the terms “guide polynucleotide/Cas endonucleasecomplex”, “guide polynucleotide/Cas endonuclease system”, “guidepolynucleotide/Cas complex”, “guide polynucleotide/Cas system”, “guidedCas system” are used interchangeably herein and refer to at least oneguide polynucleotide and at least one Cas endonuclease that are capableof forming a complex, wherein said guide polynucleotide/Cas endonucleasecomplex can direct the Cas endonuclease to a DNA target site, enablingthe Cas endonuclease to recognize, bind to, and optionally nick orcleave (introduce a single or double strand break) the DNA target site.A guide polynucleotide/Cas endonuclease complex herein can comprise Casprotein(s) and suitable polynucleotide component(s) of any of the fourknown CRISPR systems (Horvath and Barrangou, 2010, Science 327:167-170)such as a type I, II, or III CRISPR system. A Cas endonuclease unwindsthe DNA duplex at the target sequence and optionally cleaves at leastone DNA strand, as mediated by recognition of the target sequence by apolynucleotide (such as, but not limited to, a crRNA or guide RNA) thatis in complex with the Cas protein. Such recognition and cutting of atarget sequence by a Cas endonuclease typically occurs if the correctprotospacer-adjacent motif (PAM) is located at or adjacent to the 3′ endof the DNA target sequence. Alternatively, a Cas protein herein may lackDNA cleavage or nicking activity, but can still specifically bind to aDNA target sequence when complexed with a suitable RNA component. (Seealso U.S. Patent Application US 2015-0082478 A1, published on Mar. 19,2015 and US 2015-0059010 A1, published on Feb. 26, 2015, both are herebyincorporated in its entirety by reference).

A guide polynucleotide/Cas endonuclease complex can cleave one or bothstrands of a DNA target sequence. A guide polynucleotide/Casendonuclease complex that can cleave both strands of a DNA targetsequence typically comprises a Cas protein that has all of itsendonuclease domains in a functional state (e.g., wild type endonucleasedomains or variants thereof retaining some or all activity in eachendonuclease domain). Thus, a wild type Cas protein (e.g., a Cas9protein disclosed herein), or a variant thereof retaining some or allactivity in each endonuclease domain of the Cas protein, is a suitableexample of a Cas endonuclease that can cleave both strands of a DNAtarget sequence. A Cas9 protein comprising functional RuvC and HNHnuclease domains is an example of a Cas protein that can cleave bothstrands of a DNA target sequence. A guide polynucleotide/Casendonuclease complex that can cleave one strand of a DNA target sequencecan be characterized herein as having nickase activity (e.g., partialcleaving capability). A Cas nickase typically comprises one functionalendonuclease domain that allows the Cas to cleave only one strand (i.e.,make a nick) of a DNA target sequence. For example, a Cas9 nickase maycomprise (i) a mutant, dysfunctional RuvC domain and (ii) a functionalHNH domain (e.g., wild type HNH domain). As another example, a Cas9nickase may comprise (i) a functional RuvC domain (e.g., wild type RuvCdomain) and (ii) a mutant, dysfunctional HNH domain. Non-limitingexamples of Cas9 nickases suitable for use herein are disclosed in U.S.Patent Appl. Publ. No. 2014/0189896, which is incorporated herein byreference.

A pair of Cas9 nickases can be used to increase the specificity of DNAtargeting. In general, this can be done by providing two Cas9 nickasesthat, by virtue of being associated with RNA components with differentguide sequences, target and nick nearby DNA sequences on oppositestrands in the region for desired targeting. Such nearby cleavage ofeach DNA strand creates a double strand break (i.e., a DSB withsingle-stranded overhangs), which is then recognized as a substrate fornon-homologous-end-joining, NHEJ (prone to imperfect repair leading tomutations) or homologous recombination, HR. Each nick in theseembodiments can be at least about 5, 10, 15, 20, 30, 40, 50, 60, 70, 80,90, or 100 (or any integer between 5 and 100) bases apart from eachother, for example. One or two Cas9 nickase proteins herein can be usedin a Cas9 nickase pair. For example, a Cas9 nickase with a mutant RuvCdomain, but functioning HNH domain (i.e., Cas9 HNH+/RuvC−), could beused (e.g., Streptococcus pyogenes Cas9 HNH+/RuvC−). Each Cas9 nickase(e.g., Cas9 HNH+/RuvC−) would be directed to specific DNA sites nearbyeach other (up to 100 base pairs apart) by using suitable RNA componentsherein with guide RNA sequences targeting each nickase to each specificDNA site.

A Cas protein can be part of a fusion protein comprising one or moreheterologous protein domains (e.g., 1, 2, 3, or more domains in additionto the Cas protein). Such a fusion protein may comprise any additionalprotein sequence, and optionally a linker sequence between any twodomains, such as between Cas and a first heterologous domain. Examplesof protein domains that may be fused to a Cas protein herein include,without limitation, epitope tags (e.g., histidine [His], V5, FLAG,influenza hemagglutinin [HA], myc, VSV-G, thioredoxin [Trx]), reporters(e.g., glutathione-5-transferase [GST], horseradish peroxidase [HRP],chloramphenicol acetyltransferase [CAT], beta-galactosidase,beta-glucuronidase [GUS], luciferase, green fluorescent protein [GFP],HcRed, DsRed, cyan fluorescent protein [CFP], yellow fluorescent protein[YFP], blue fluorescent protein [BFP]), and domains having one or moreof the following activities: methylase activity, demethylase activity,transcription activation activity (e.g., VP16 or VP64), transcriptionrepression activity, transcription release factor activity, histonemodification activity, RNA cleavage activity and nucleic acid bindingactivity. A Cas protein can also be in fusion with a protein that bindsDNA molecules or other molecules, such as maltose binding protein (MBP),S-tag, Lex A DNA binding domain (DBD), GAL4A DNA binding domain, andherpes simplex virus (HSV) VP16.

A Cas protein herein can be from any of the following genera: Aeropyrum,Pyrobaculum, Sulfolobus, Archaeoglobus, Haloarcula, Methanobacteriumn,Methanococcus, Methanosarcina, Methanopyrus, Pyrococcus, Picrophilus,Thernioplasnia, Corynebacterium, Mycobacterium, Streptomyces, Aquifrx,Porphvromonas, Chlorobium, Thermus, Bacillus, Listeria, Staphylococcus,Clostridium, Thermoanaerobacter, Mycoplasma, Fusobacterium, Azarcus,Chromobacterium, Neisseria, Nitrosomonas, Desulfovibrio, Geobacter,Myrococcus, Campylobacter, Wolinella, Acinetobacter, Erwinia,Escherichia, Legionella, Methylococcus, Pasteurella, Photobacterium,Salmonella, Xanthomonas, Yersinia, Streptococcus, Treponema,Francisella, or Thermotoga. See also U.S. patent applications 62/162,377filed May 15, 2015 and 62/162,353 filed May 15, 2015 (both applicationsincorporated herein by reference) for more examples of Cas proteins.

A guide polynucleotide/Cas endonuclease complex in certain embodimentscan bind to a DNA target site sequence, but does not cleave any strandat the target site sequence. Such a complex may comprise a Cas proteinin which all of its nuclease domains are mutant, dysfunctional. Forexample, a Cas9 protein herein that can bind to a DNA target sitesequence, but does not cleave any strand at the target site sequence,may comprise both a mutant, dysfunctional RuvC domain and a mutant,dysfunctional HNH domain. A Cas protein herein that binds, but does notcleave, a target DNA sequence can be used to modulate gene expression,for example, in which case the Cas protein could be fused with atranscription factor (or portion thereof) (e.g., a repressor oractivator, such as any of those disclosed herein). In other aspects, aninactivated Cas protein may be fused with another protein havingendonuclease activity, such as a Fok I endonuclease.

The Cas endonuclease gene herein can encode a Type II Cas9 endonuclease,such as but not limited to, Cas9 genes listed in SEQ ID NOs: 462, 474,489, 494, 499, 505, and 518 of WO2007/025097, published March 1, 2007,and incorporated herein by reference. In another embodiment, the Casendonuclease gene is a microbe or optimized Cas9 endonuclease gene. TheCas endonuclease gene can be operably linked to a SV40 nuclear targetingsignal upstream of the Cas codon region and a bipartite VirD2 nuclearlocalization signal (Tinland et al. (1992) Proc. Natl. Acad. Sci. USA89:7442-6) downstream of the Cas codon region.

The Cas endonuclease gene includes a plant or microbial codon optimizedStreptococcus pyogenes Cas9 gene that can recognize any genomic sequenceof the form N(12-30)NGG can in principle be targeted or a Cas9endonuclease originated from an organism selected from the groupconsisting of Brevibacillus laterosporus, Lactobacillus reuteri MIc3,Lactobacillus rossiae DSM 15814, Pediococcus pentosaceus SL4,Lactobacillus nodensis JCM 14932, Sulfurospirillum sp. SCADC,Bifidobacterium thermophilum DSM 20210, Loktanella vestfoldensis,Sphingomonas sanxanigenens NX02, Epilithonimonas tenax DSM 16811,Sporocytophaga myxococcoides and Psychroflexus torquis ATCC 700755,wherein said Cas9 endonuclease can form a guide RNA/Cas endonucleasecomplex capable of recognizing, binding to, and optionally nicking orcleaving all or part of a DNA target sequence. Other Cas endonucleasesystems have been described in U.S. patent applications 62/162,377 filedMay 15, 2015 and 62/162,353 filed May 15, 2015, both applicationsincorporated herein by reference.

“Cas9” (formerly referred to as Cas5, Csn1, or Csx12) herein refers to aCas endonuclease of a type II CRISPR system that forms a complex with acrNucleotide and a tracrNucleotide, or with a single guidepolynucleotide, for specifically recognizing and cleaving all or part ofa DNA target sequence. Cas9 protein comprises a RuvC nuclease domain andan HNH (H-N-H) nuclease domain, each of which can cleave a single DNAstrand at a target sequence (the concerted action of both domains leadsto DNA double-strand cleavage, whereas activity of one domain leads to anick). In general, the RuvC domain comprises subdomains I, II and III,where domain I is located near the N-terminus of Cas9 and subdomains IIand III are located in the middle of the protein, flanking the HNHdomain (Hsu et al, Cell 157:1262-1278). A type II CRISPR system includesa DNA cleavage system utilizing a Cas9 endonuclease in complex with atleast one polynucleotide component. For example, a Cas9 can be incomplex with a CRISPR RNA (crRNA) and a trans-activating CRISPR RNA(tracrRNA). In another example, a Cas9 can be in complex with a singleguide RNA.

The amino acid sequence of a Cas9 protein described herein, as well ascertain other Cas proteins herein, may be derived from a Streptococcus(e.g., S. pyogenes, S. pneumoniae, S. thermophilus, S. agalactiae, S.parasanguinis, S. oralis, S. salivarius, S. macacae, S. dysgalactiae, S.anginosus, S. constellatus, S. pseudoporcinus, S. mutans), Listeria(e.g., L. innocua), Spiroplasma (e.g., S. apis, S. syrphidicola),Peptostreptococcaceae, Atopobium, Porphyromonas (e.g., P. catoniae),Prevotella (e.g., P. intermedia), Veillonella, Treponema (e.g., T.socranskii, T. denticola), Capnocytophaga, Finegoldia (e.g., F. magna),Coriobacteriaceae (e.g., C. bacterium), Olsenella (e.g., O. profusa),Haemophilus (e.g., H. sputorum, H. pittmaniae), Pasteurella (e.g., P.bettyae), Olivibacter (e.g., O. sitiensis), Epilithonimonas (e.g., E.tenax), Mesonia (e.g., M. mobilis), Lactobacillus (e.g., L. plantarum),Bacillus (e.g., B. cereus), Aquimarina (e.g., A. muelleri),Chryseobacterium (e.g., C. palustre), Bacteroides (e.g., B.graminisolvens), Neisseria (e.g., N. meningitidis), Francisella (e.g.,F. novicida), or Flavobacterium (e.g., F. frigidarium, F. soli) species,for example. As another example, a Cas9 protein can be any of the Cas9proteins disclosed in Chylinski et al. (RNA Biology 10:726-737 and U.S.patent application 62/162377, filed May 15, 2015), which areincorporated herein by reference.

Accordingly, the sequence of a Cas9 protein herein can comprise, forexample, any of the Cas9 amino acid sequences disclosed in GenBankAccession Nos. G3ECR1 (S. thermophilus), WP_026709422, WP_027202655,WP_027318179, WP_027347504, WP_027376815, WP_027414302, WP_027821588,WP_027886314, WP_027963583, WP_028123848, WP_028298935, Q03JI6 (S.thermophilus), EGP66723, EGS38969, EGV05092, EHI65578 (S.pseudoporcinus), EIC75614 (S. oralis), EID22027 (S. constellatus),EIJ69711, EJP22331 (S. oralis), EJP26004 (S. anginosus), EJP30321,EPZ44001 (S. pyogenes), EPZ46028 (S. pyogenes), EQL78043 (S. pyogenes),EQL78548 (S. pyogenes), ERL10511, ERL12345, ERL19088 (S. pyogenes),ESA57807 (S. pyogenes), ESA59254 (S. pyogenes), ESU85303 (S. pyogenes),ETS96804, UC75522, EGR87316 (S. dysgalactiae), EGS33732, EGV01468 (S.oralis), EHJ52063 (S. macacae), EID26207 (S. oralis), EID33364, EIG27013(S. parasanguinis), EJF37476, EJO19166 (Streptococcus sp. BS35b),EJU16049, EJU32481, YP_006298249, ERF61304, ERK04546, ETJ95568 (S.agalactiae), TS89875, ETS90967 (Streptococcus sp. SR4), ETS92439,EUB27844 (Streptococcus sp. BS21), AFJ08616, EUC82735 (Streptococcus sp.CM6), EWC92088, EWC94390, EJP25691, YP_008027038, YP_008868573,AGM26527, AHK22391, AHB36273, Q927P4, G3ECR1, or Q99ZW2 (S. pyogenes),which are incorporated by reference. A variant of any of these Cas9protein sequences may be used, but should have specific bindingactivity, and optionally endonucleolytic activity, toward DNA whenassociated with an RNA component herein. Such a variant may comprise anamino acid sequence that is at least about 80%, 81%, 82%, 83%, 84%, 85%,86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%identical to the amino acid sequence of the reference Cas9.

Alternatively, a Cas9 protein may comprise an amino acid sequence thatis at least about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical to any of theforegoing amino acid sequences, for example. Such a variant Cas9 proteinshould have specific binding activity, and optionally cleavage ornicking activity, toward DNA when associated with an RNA componentherein.

A Cas protein herein such as a Cas9 can comprise a heterologous nuclearlocalization sequence (NLS). A heterologous NLS amino acid sequenceherein may be of sufficient strength to drive accumulation of a Casprotein in a detectable amount in the nucleus of a yeast cell herein,for example. An NLS may comprise one (monopartite) or more (e.g.,bipartite) short sequences (e.g., 2 to 20 residues) of basic, positivelycharged residues (e.g., lysine and/or arginine), and can be locatedanywhere in a Cas amino acid sequence but such that it is exposed on theprotein surface. An NLS may be operably linked to the N-terminus orC-terminus of a Cas protein herein, for example. Two or more NLSsequences can be linked to a Cas protein, for example, such as on boththe N- and C-termini of a Cas protein. Non-limiting examples of suitableNLS sequences herein include those disclosed in U.S. Pat. No.7,309,576,which is incorporated herein by reference.

The Cas endonuclease can comprise a modified form of the Cas9polypeptide. The modified form of the Cas9 polypeptide can include anamino acid change (e.g., deletion, insertion, or substitution) thatreduces the naturally-occurring nuclease activity of the Cas9 protein.For example, in some instances, the modified form of the Cas9 proteinhas less than 50%, less than 40%, less than 30%, less than 20%, lessthan 10%, less than 5%, or less than 1% of the nuclease activity of thecorresponding wild-type Cas9 polypeptide (US patent applicationUS20140068797 A1, published on Mar. 6, 2014). In some cases, themodified form of the Cas9 polypeptide has no substantial nucleaseactivity and is referred to as catalytically “inactivated Cas9” or“deactivated cas9 (dCas9).” Catalytically inactivated Cas9 variantsinclude Cas9 variants that contain mutations in the HNH and RuvCnuclease domains. These catalytically inactivated Cas9 variants arecapable of interacting with sgRNA and binding to the target site in vivobut cannot cleave either strand of the target DNA.

A catalytically inactive Cas9 can be fused to a heterologous sequence(US patent application US20140068797 A1, published on Mar. 6, 2014).Suitable fusion partners include, but are not limited to, a polypeptidethat provides an activity that indirectly increases transcription byacting directly on the target DNA or on a polypeptide (e.g., a histoneor other DNA-binding protein) associated with the target DNA. Additionalsuitable fusion partners include, but are not limited to, a polypeptidethat provides for methyltransferase activity, demethylase activity,acetyltransferase activity, deacetylase activity, kinase activity,phosphatase activity, ubiquitin ligase activity, deubiquitinatingactivity, adenylation activity, deadenylation activity, SUMOylatingactivity, deSUMOylating activity, ribosylation activity, deribosylationactivity, myristoylation activity, or demyristoylation activity. Furthersuitable fusion partners include, but are not limited to, a polypeptidethat directly provides for increased transcription of the target nucleicacid (e.g., a transcription activator or a fragment thereof, a proteinor fragment thereof that recruits a transcription activator, a smallmolecule/drug-responsive transcription regulator, etc.). A catalyticallyinactive Cas9 can also be fused to a Fok I nuclease to generate doublestrand breaks (Guilinger et al. 2014. Nature Biotechnology, 32(6).

The terms “functional fragment “, “fragment that is functionallyequivalent” and “functionally equivalent fragment” of a Cas endonucleaseare used interchangeably herein, and refer to a portion or subsequenceof the Cas endonuclease sequence of the present disclosure in which theability to recognize, bind to, and optionally nick or cleave (introducea single or double strand break in) the target site is retained.

The terms “functional variant ”, “Variant that is functionallyequivalent” and “functionally equivalent variant” of a Cas endonucleaseare used interchangeably herein, and refer to a variant of the Casendonuclease of the present disclosure in which the ability torecognize, bind to, and optionally nick or cleave (introduce a single ordouble strand break in) the target site is retained. Fragments andvariants can be obtained via methods such as site-directed mutagenesisand synthetic construction.

Any guided endonuclease can be used in the methods disclosed herein.Such endonucleases include, but are not limited to Cas9 and Cpf1endonucleases. Many endonucleases have been described to date that canrecognize specific PAM sequences (see for example, Jinek et al. 2012.Science 337:816-821, U.S. patent application 62/162377 filed May 15,2015 and U.S. patent application 62/162353 filed May 15, 2015 andZetsche B et al. 2015. Cell 163:1013) and cleave the target DNA at aspecific positions. It is understood that based on the methods andembodiments described herein utilizing a guided Cas system one can nowtailor these methods such that they can utilize any guided endonucleasesystem.

The endonuclease can be provided to a cell by any method known in theart, for example, but not limited to transient introduction methods,transfection, microinjection, and/or topical application or indirectlyvia recombination constructs. The endonuclease can be provided as aprotein or as a guided polynucleotide complex directly to a cell orindirectly via recombination constructs. The endonuclease can beintroduced into a cell transiently or can be incorporated into thegenome of the host cell using any method known in the art. Uptake of theendonuclease and/or the guided polynucleotide into the cell can befacilitated with a Cell Penetrating Peptide (CPP) as described in U.S.application 62/075999, filed Nov. 6, 2014.

As used herein, the term “guide polynucleotide”, relates to apolynucleotide sequence that can form a complex with a Cas endonucleaseand enables the Cas endonuclease to recognize, bind to, and optionallycleave a DNA target site. The guide polynucleotide can be a singlemolecule or a double molecule. The guide polynucleotide sequence can bea RNA sequence, a DNA sequence, or a combination thereof (a RNA-DNAcombination sequence). Optionally, the guide polynucleotide can compriseat least one nucleotide, phosphodiester bond or linkage modificationsuch as, but not limited, to Locked Nucleic Acid (LNA), 5-methyl dC,2,6-Diaminopurine, 2′-Fluoro A, 2′-Fluoro U, 2′-O-Methyl RNA,phosphorothioate bond, linkage to a cholesterol molecule, linkage to apolyethylene glycol molecule, linkage to a spacer 18 (hexaethyleneglycol chain) molecule, or 5′ to 3′ covalent linkage resulting incircularization. A guide polynucleotide that solely comprisesribonucleic acids is also referred to as a “guide RNA” or “gRNA” (Seealso U.S. Patent Application US 2015-0082478 A1, published on Mar. 19,2015 and US 2015-0059010 A1, published on Feb. 26, 2015, both are herebyincorporated in its entirety by reference).

The guide polynucleotide can be a double molecule (also referred to asduplex guide polynucleotide) comprising a crNucleotide sequence and atracrNucleotide sequence. The crNucleotide includes a first nucleotidesequence domain (referred to as Variable Targeting domain or VT domain)that can hybridize to a nucleotide sequence in a target DNA and a secondnucleotide sequence (also referred to as a tracr mate sequence) that ispart of a Cas endonuclease recognition (CER) domain. The tracr matesequence can hybridized to a tracrNucleotide along a region ofcomplementarity and together form the Cas endonuclease recognitiondomain or CER domain. The CER domain is capable of interacting with aCas endonuclease polypeptide. The crNucleotide and the tracrNucleotideof the duplex guide polynucleotide can be RNA, DNA, and/orRNA-DNA-combination sequences. In some embodiments, the crNucleotidemolecule of the duplex guide polynucleotide is referred to as “crDNA”(when composed of a contiguous stretch of DNA nucleotides) or “crRNA”(when composed of a contiguous stretch of RNA nucleotides), or“crDNA-RNA” (when composed of a combination of DNA and RNA nucleotides).The crNucleotide can comprise a fragment of the cRNA naturally occurringin Bacteria and Archaea. The size of the fragment of the cRNA naturallyoccurring in Bacteria and Archaea that can be present in a crNucleotidedisclosed herein can range from, but is not limited to, 2, 3, 4, 5, 6,7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more nucleotides.In some embodiments the tracrNucleotide is referred to as “tracrRNA”(when composed of a contiguous stretch of RNA nucleotides) or “tracrDNA”(when composed of a contiguous stretch of DNA nucleotides) or“tracrDNA-RNA” (when composed of a combination of DNA and RNAnucleotides. In one embodiment, the RNA that guides the RNA/Cas9endonuclease complex is a duplexed RNA comprising a duplexcrRNA-tracrRNA.

The tracrRNA (trans-activating CRISPR RNA) contains, in the 5′-to-3′direction, (i) a sequence that anneals with the repeat region of CRISPRtype II crRNA and (ii) a stem loop-containing portion (Deltcheva et al.,Nature 471:602-607). The duplex guide polynucleotide can form a complexwith a Cas endonuclease, wherein said guide polynucleotide/Casendonuclease complex (also referred to as a guide polynucleotide/Casendonuclease system) can direct the Cas endonuclease to a genomic targetsite, enabling the Cas endonuclease to recognize, bind to, andoptionally nick or cleave (introduce a single or double strand break)into the target site. (See also U.S. Patent Application US 2015-0082478A1, published on Mar. 19, 2015 and US 2015-0059010 A1, published on Feb.26, 2015, both are hereby incorporated in its entirety by reference.)

The guide polynucleotide can also be a single molecule (also referred toas single guide polynucleotide) comprising a crNucleotide sequencelinked to a tracrNucleotide sequence. The single guide polynucleotidecomprises a first nucleotide sequence domain (referred to as VariableTargeting domain or VT domain) that can hybridize to a nucleotidesequence in a target DNA and a Cas endonuclease recognition domain (CERdomain), that interacts with a Cas endonuclease polypeptide. By “domain”it is meant a contiguous stretch of nucleotides that can be RNA, DNA,and/or RNA-DNA-combination sequence. The VT domain and/or the CER domainof a single guide polynucleotide can comprise a RNA sequence, a DNAsequence, or a RNA-DNA-combination sequence. The single guidepolynucleotide being comprised of sequences from the crNucleotide andthe tracrNucleotide may be referred to as “single guide RNA” (whencomposed of a contiguous stretch of RNA nucleotides) or “single guideDNA” (when composed of a contiguous stretch of DNA nucleotides) or“single guide RNA-DNA” (when composed of a combination of RNA and DNAnucleotides). The single guide polynucleotide can form a complex with aCas endonuclease, wherein said guide polynucleotide/Cas endonucleasecomplex (also referred to as a guide polynucleotide/Cas endonucleasesystem) can direct the Cas endonuclease to a genomic target site,enabling the Cas endonuclease to recognize, bind to, and optionally nickor cleave (introduce a single or double strand break) the target site.(See also U.S. Patent Application US 2015-0082478 A1, published on Mar.19, 2015 and US 2015-0059010 A1, published on Feb. 26, 2015, both arehereby incorporated in its entirety by reference.)

The term “variable targeting domain” or “VT domain” is usedinterchangeably herein and includes a nucleotide sequence that canhybridize (is complementary) to one strand (nucleotide sequence) of adouble strand DNA target site. The % complementation between the firstnucleotide sequence domain (VT domain) and the target sequence can be atleast 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%,63%, 63%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%,77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100%. The variabletargeting domain can be at least 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,22, 23, 24, 25, 26, 27, 28, 29 or 30 nucleotides in length. In someembodiments, the variable targeting domain comprises a contiguousstretch of 12 to 30 nucleotides. The variable targeting domain can becomposed of a DNA sequence, a RNA sequence, a modified DNA sequence, amodified RNA sequence, or any combination thereof.

The term “Cas endonuclease recognition domain” or “CER domain” (of aguide polynucleotide) is used interchangeably herein and includes anucleotide sequence that interacts with a Cas endonuclease polypeptide.A CER domain comprises a tracrNucleotide mate sequence followed by atracrNucleotide sequence. The CER domain can be composed of a DNAsequence, a RNA sequence, a modified DNA sequence, a modified RNAsequence (see for example US 2015-0059010 A1, published on Feb. 26,2015, incorporated in its entirety by reference herein), or anycombination thereof.

The nucleotide sequence linking the crNucleotide and the tracrNucleotideof a single guide polynucleotide can comprise a RNA sequence, a DNAsequence, or a RNA-DNA combination sequence. In one embodiment, thenucleotide sequence linking the crNucleotide and the tracrNucleotide ofa single guide polynucleotide can be at least 3, 4, 5, 6, 7, 8, 9, 10,11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46,47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64,65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 78, 79, 80, 81,82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99or 100 nucleotides in length. In another embodiment, the nucleotidesequence linking the crNucleotide and the tracrNucleotide of a singleguide polynucleotide can comprise a tetraloop sequence, such as, but notlimiting to a GAAA tetraloop sequence.

Nucleotide sequence modification of the guide polynucleotide, VT domainand/or CER domain can be selected from, but not limited to, the groupconsisting of a 5′ cap, a 3′ polyadenylated tail, a riboswitch sequence,a stability control sequence, a sequence that forms a dsRNA duplex, amodification or sequence that targets the guide poly nucleotide to asubcellular location, a modification or sequence that provides fortracking, a modification or sequence that provides a binding site forproteins, a Locked Nucleic Acid (LNA), a 5-methyl dC nucleotide, a2,6-Diaminopurine nucleotide, a 2′-Fluoro A nucleotide, a 2′-Fluoro Unucleotide; a 2′-O-Methyl RNA nucleotide, a phosphorothioate bond,linkage to a cholesterol molecule, linkage to a polyethylene glycolmolecule, linkage to a spacer 18 molecule, a 5′ to 3′ covalent linkage,or any combination thereof. These modifications can result in at leastone additional beneficial feature, wherein the additional beneficialfeature is selected from the group of a modified or regulated stability,a subcellular targeting, tracking, a fluorescent label, a binding sitefor a protein or protein complex, modified binding affinity tocomplementary target sequence, modified resistance to cellulardegradation, and increased cellular permeability.

The terms “functional fragment ”, “fragment that is functionallyequivalent” and “functionally equivalent fragment” of a guide RNA, crRNAor tracrRNA are used interchangeably herein, and refer to a portion orsubsequence of the guide RNA, crRNA or tracrRNA, respectively, of thepresent disclosure in which the ability to function as a guide RNA,crRNA or tracrRNA, respectively, is retained.

The terms “functional variant ”, “Variant that is functionallyequivalent” and “functionally equivalent variant” of a guide RNA, crRNAor tracrRNA (respectively) are used interchangeably herein, and refer toa variant of the guide RNA, crRNA or tracrRNA, respectively, of thepresent disclosure in which the ability to function as a guide RNA,crRNA or tracrRNA, respectively, is retained.

The terms “single guide RNA” and “sgRNA” are used interchangeably hereinand relate to a synthetic fusion of two RNA molecules, a crRNA (CRISPRRNA) comprising a variable targeting domain (linked to a tracr matesequence that hybridizes to a tracrRNA), fused to a tracrRNA(trans-activating CRISPR RNA). The single guide RNA can comprise a crRNAor crRNA fragment and a tracrRNA or tracrRNA fragment of the type IICRISPR/Cas system that can form a complex with a type II Casendonuclease, wherein said guide RNA/Cas endonuclease complex can directthe Cas endonuclease to a DNA target site, enabling the Cas endonucleaseto recognize, bind to, and optionally nick or cleave (introduce a singleor double strand break) the DNA target site.

The terms “guide RNA/Cas endonuclease complex”, “guide RNA/Casendonuclease system”, “guide RNA/Cas complex”, “guide RNA/Cas system”,“gRNA/Cas complex”, “gRNA/Cas system”, “RNA-guided endonuclease”, “RGEN”are used interchangeably herein and refer to at least one RNA componentand at least one Cas endonuclease that are capable of forming a complex,wherein said guide RNA/Cas endonuclease complex can direct the Casendonuclease to a DNA target site, enabling the Cas endonuclease torecognize, bind to, and optionally nick or cleave (introduce a single ordouble strand break) the DNA target site. A guide RNA/Cas endonucleasecomplex herein can comprise Cas protein(s) and suitable RNA component(s)of any of the four known CRISPR systems (Horvath and Barrangou, 2010,Science 327:167-170) such as a type I, II, or III CRISPR system. A guideRNA/Cas endonuclease complex can comprise a Type II Cas9 endonucleaseand at least one RNA component (e.g., a crRNA and tracrRNA, or a gRNA).(See also U.S. Patent Application US 2015-0082478 A1, published on Mar.19, 2015 and US 2015-0059010 A1, published on Feb. 26, 2015, both arehereby incorporated in its entirety by reference).

The guide polynucleotide can be introduced into a cell transiently, assingle stranded polynucleotide or a double stranded polynucleotide,using any method known in the art such as, but not limited to, particlebombardment, Agrobacterium transformation or topical applications. Theguide polynucleotide can also be introduced indirectly into a cell byintroducing a recombinant DNA molecule (via methods such as, but notlimited to, particle bombardment or Agrobacterium transformation)comprising a heterologous nucleic acid fragment encoding a guidepolynucleotide, operably linked to a specific promoter that is capableof transcribing the guide RNA in said cell. The specific promoter canbe, but is not limited to, a RNA polymerase III promoter, which allowfor transcription of RNA with precisely defined, unmodified, 5′- and3′-ends (DiCarlo et al. 2013. Nucleic Acids Res. 41: 4336-4343; Ma etal. 2014. Mol. Ther. Nucleic Acids 3:e161) as described in U.S.application 62/036652, filed on Aug. 13, 2014, incorporated herein inits entirety by reference.

The terms “target site”, “target sequence”, “target site sequence,“target DNA”, “target locus”, “genomic target site”, “genomic targetsequence”, “genomic target locus” and “protospacer”, are usedinterchangeably herein and refer to a polynucleotide sequence such as,but not limited to, a nucleotide sequence on a chromosome, episome, orany other DNA molecule in the genome (including chromosomal,choloroplastic, mitochondrial DNA, plasmid DNA) of a cell, at which aguide polynucleotide/Cas endonuclease complex can recognize, bind to,and optionally nick or cleave. The target site can be an endogenous sitein the genome of a cell, or alternatively, the target site can beheterologous to the cell and thereby not be naturally occurring in thegenome of the cell, or the target site can be found in a heterologousgenomic location compared to where it occurs in nature. As used herein,terms “endogenous target sequence” and “native target sequence” are usedinterchangeable herein to refer to a target sequence that is endogenousor native to the genome of a cell and is at the endogenous or nativeposition of that target sequence in the genome of the cell. Cellsinclude, but are not limited to, human, non-human, animal, bacterial,fungal, insect, yeast, non-conventional yeast, and plant cells as wellas plants and seeds produced by the methods described herein. An“artificial target site” or “artificial target sequence” are usedinterchangeably herein and refer to a target sequence that has beenintroduced into the genome of a cell. Such an artificial target sequencecan be identical in sequence to an endogenous or native target sequencein the genome of a cell but be located in a different position (i.e., anon-endogenous or non-native position) in the genome of a cell.

An “altered target site”, “altered target sequence”, “modified targetsite”, “modified target sequence” are used interchangeably herein andrefer to a target sequence as disclosed herein that comprises at leastone nucleic acid alteration when compared to non-altered targetsequence. Such “nucleic acid alterations” include, for example: (i)replacement of at least one nucleotide, (ii) a deletion of at least onenucleotide, (iii) an insertion of at least one nucleotide, or (iv) anycombination of (i)-(iii).

Methods for “modifying a target site” and “altering a target site” areused interchangeably herein and refer to methods for producing analtered target site.

The length of the target DNA sequence (target site) can vary, andincludes, for example, target sites that are at least 12, 13, 14, 15,16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or morenucleotides in length. It is further possible that the target site canbe palindromic, that is, the sequence on one strand reads the same inthe opposite direction on the complementary strand. The nick/cleavagesite can be within the target sequence or the nick/cleavage site couldbe outside of the target sequence. In another variation, the cleavagecould occur at nucleotide positions immediately opposite each other toproduce a blunt end cut or, in other Cases, the incisions could bestaggered to produce single-stranded overhangs, also called “stickyends”, which can be either 5′ overhangs, or 3′ overhangs. Activevariants of genomic target sites can also be used. Such active variantscan comprise at least 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%,95%, 96%, 97%, 98%, 99% or more sequence identity to the given targetsite, wherein the active variants retain biological activity and henceare capable of being recognized and cleaved by an Cas endonuclease.Assays to measure the single or double-strand break of a target site byan endonuclease are known in the art and generally measure the overallactivity and specificity of the agent on DNA substrates containingrecognition sites.

A “protospacer adjacent motif” (PAM) herein refers to a short nucleotidesequence adjacent to a target sequence (protospacer) that is recognized(targeted) by a guide polynucleotide/Cas endonuclease system describedherein. The Cas endonuclease may not successfully recognize a target DNAsequence if the target DNA sequence is not followed by a PAM sequence.The sequence and length of a PAM herein can differ depending on the Casprotein or Cas protein complex used. The PAM sequence can be of anylength but is typically 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19 or 20 nucleotides long.

The terms “targeting”, “gene targeting” and “DNA targeting” are usedinterchangeably herein. DNA targeting herein may be the specificintroduction of a knock-out, edit, or knock-in at a particular DNAsequence, such as in a chromosome or plasmid of a cell. In general, DNAtargeting can be performed herein by cleaving one or both strands at aspecific DNA sequence in a cell with an endonuclease associated with asuitable polynucleotide component. Such DNA cleavage, if a double-strandbreak (DSB), can prompt NHEJ or HDR processes which can lead tomodifications at the target site.

A targeting method herein can be performed in such a way that two ormore DNA target sites are targeted in the method, for example. Such amethod can optionally be characterized as a multiplex method. Two,three, four, five, six, seven, eight, nine, ten, or more target sitescan be targeted at the same time in certain embodiments. A multiplexmethod is typically performed by a targeting method herein in whichmultiple different RNA components are provided, each designed to guidean guidepolynucleotide/Cas endonuclease complex to a unique DNA targetsite.

The terms “knock-out”, “gene knock-out” and “genetic knock-out” are usedinterchangeably herein. A knock-out represents a DNA sequence of a cellthat has been rendered partially or completely inoperative by targetingwith a Cas protein; such a DNA sequence prior to knock-out could haveencoded an amino acid sequence, or could have had a regulatory function(e.g., promoter), for example. A knock-out may be produced by an indel(insertion or deletion of nucleotide bases in a target DNA sequencethrough NHEJ), or by specific removal of sequence that reduces orcompletely destroys the function of sequence at or near the targetingsite.

The guide polynucleotide/Cas endonuclease system can be used incombination with a co-delivered polynucleotide modification template toallow for editing (modification) of a genomic nucleotide sequence ofinterest. (See also U.S. Patent Application US 2015-0082478 A1,published on Mar. 19, 2015 and WO2015/026886 A1, published on Feb. 26,2015, both are hereby incorporated in its entirety by reference.)

A “modified nucleotide” or “edited nucleotide” refers to a nucleotidesequence of interest that comprises at least one alteration whencompared to its non-modified nucleotide sequence. Such “alterations”include, for example: (i) replacement of at least one nucleotide, (ii) adeletion of at least one nucleotide, (iii) an insertion of at least onenucleotide, or (iv) any combination of (i)-(iii).

The term “polynucleotide modification template” includes apolynucleotide that comprises at least one nucleotide modification whencompared to the nucleotide sequence to be edited. A nucleotidemodification can be at least one nucleotide substitution, addition ordeletion. Optionally, the polynucleotide modification template canfurther comprise homologous nucleotide sequences flanking the at leastone nucleotide modification, wherein the flanking homologous nucleotidesequences provide sufficient homology to the desired nucleotide sequenceto be edited.

Genome editing can be accomplished using any method of gene editingavailable. For example, gene editing can be accomplished through theintroduction into a host cell of a polynucleotide modification template(sometimes also referred to as a gene repair oligonucleotide) containinga targeted modification to a gene within the genome of the host cell.The polynucleotide modification template for use in such methods can beeither single-stranded or double-stranded. Examples of such methods aregenerally described, for example, in US Publication No. 2013/0019349.

In some embodiments, gene editing may be facilitated through theinduction of a double-stranded break (DSB) in a defined position in thegenome near the desired alteration. DSBs can be induced using anyDSB-inducing agent available, including, but not limited to, TALENs,meganucleases, zinc finger nucleases, Cas9-gRNA systems (based onbacterial CRISPR-Cas systems), and the like. In some embodiments, theintroduction of a DSB can be combined with the introduction of apolynucleotide modification template.

The process for editing a genomic sequence combining DSB andmodification templates generally comprises: providing to a host cell, aDSB-inducing agent, or a nucleic acid encoding a DSB-inducing agent,that recognizes a target sequence in the chromosomal sequence and isable to induce a DSB in the genomic sequence, and at least onepolynucleotide modification template comprising at least one nucleotidealteration when compared to the nucleotide sequence to be edited. Thepolynucleotide modification template can further comprise nucleotidesequences flanking the at least one nucleotide alteration, in which theflanking sequences are substantially homologous to the chromosomalregion flanking the DSB. Genome editing using DSB-inducing agents, suchas Cas9-gRNA complexes, has been described, for example in U.S. PatentApplication US 2015-0082478 A1, published on Mar. 19, 2015,WO2015/026886 A1, published on Feb. 26, 2015, U.S. application62/023246, filed on Jul. 07, 2014, and U.S. application 62/036,652,filed on Aug. 13, 2014, all of which are incorporated by referenceherein.

The terms “knock-in”, “gene knock-in, “gene insertion” and “geneticknock-in” are used interchangeably herein. A knock-in represents thereplacement or insertion of a DNA sequence at a specific DNA sequence incell by targeting with a Cas protein (by HR, wherein a suitable donorDNA polynucleotide is also used). Examples of knock-ins are a specificinsertion of a heterologous amino acid coding sequence in a codingregion of a gene, or a specific insertion of a transcriptionalregulatory element in a genetic locus.

Various methods and compositions can be employed to obtain a cell ororganism having a polynucleotide of interest inserted in a target sitefor a Cas endonuclease. Such methods can employ homologous recombinationto provide integration of the polynucleotide of Interest at the targetsite. In one method provided, a polynucleotide of interest is providedto the organism cell in a donor DNA construct. As used herein, “donorDNA” is a DNA construct that comprises a polynucleotide of Interest tobe inserted into the target site of a Cas endonuclease. The donor DNAconstruct further comprises a first and a second region of homology thatflank the polynucleotide of Interest. The first and second regions ofhomology of the donor DNA share homology to a first and a second genomicregion, respectively, present in or flanking the target site of the cellor organism genome. By “homology” is meant DNA sequences that aresimilar. For example, a “region of homology to a genomic region” that isfound on the donor DNA is a region of DNA that has a similar sequence toa given “genomic region” in the cell or organism genome. A region ofhomology can be of any length that is sufficient to promote homologousrecombination at the cleaved target site. For example, the region ofhomology can comprise at least 5-10, 5-15, 5-20, 5-25, 5-30, 5-35, 5-40,5-45, 5-50, 5-55, 5-60, 5-65, 5-70, 5-75, 5-80, 5-85, 5-90, 5-95, 5-100,5-200, 5-300, 5-400, 5-500, 5-600, 5-700, 5-800, 5-900, 5-1000, 5-1100,5-1200, 5-1300, 5-1400, 5-1500, 5-1600, 5-1700, 5-1800, 5-1900, 5-2000,5-2100, 5-2200, 5-2300, 5-2400, 5-2500, 5-2600, 5-2700, 5-2800, 5-2900,5-3000, 5-3100 or more bases in length such that the region of homologyhas sufficient homology to undergo homologous recombination with thecorresponding genomic region. “Sufficient homology” indicates that twopolynucleotide sequences have sufficient structural similarity to act assubstrates for a homologous recombination reaction. The structuralsimilarity includes overall length of each polynucleotide fragment, aswell as the sequence similarity of the polynucleotides. Sequencesimilarity can be described by the percent sequence identity over thewhole length of the sequences, and/or by conserved regions comprisinglocalized similarities such as contiguous nucleotides having 100%sequence identity, and percent sequence identity over a portion of thelength of the sequences.

The amount of homology or sequence identity shared by a target and adonor polynucleotide can vary and includes total lengths and/or regionshaving unit integral values in the ranges of about 1-20 bp, 20-50 bp,50-100 bp, 75-150 bp, 100-250 bp, 150-300 bp, 200-400 bp, 250-500 bp,300-600 bp, 350-750 bp, 400-800 bp, 450-900 bp, 500-1000 bp, 600-1250bp, 700-1500 bp, 800-1750 bp, 900-2000 bp, 1-2.5 kb, 1.5-3 kb, 2-4 kb,2.5-5 kb, 3-6 kb, 3.5-7 kb, 4-8 kb, 5-10 kb, or up to and including thetotal length of the target site. These ranges include every integerwithin the range, for example, the range of 1-20 bp includes 1, 2, 3, 4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20 bps. Theamount of homology can also described by percent sequence identity overthe full aligned length of the two polynucleotides which includespercent sequence identity of about at least 50%, 55%, 60%, 65%, 70%,71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%,85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%,99% or 100%. Sufficient homology includes any combination ofpolynucleotide length, global percent sequence identity, and optionallyconserved regions of contiguous nucleotides or local percent sequenceidentity, for example sufficient homology can be described as a regionof 75-150 bp having at least 80% sequence identity to a region of thetarget locus. Sufficient homology can also be described by the predictedability of two polynucleotides to specifically hybridize under highstringency conditions, see, for example, Sambrook et al., (1989)Molecular Cloning: A Laboratory Manual, (Cold Spring Harbor LaboratoryPress, NY); Current Protocols in Molecular Biology, Ausubel et al., Eds(1994) Current Protocols, (Greene Publishing Associates, Inc. and JohnWiley & Sons, Inc.); and, Tijssen (1993) Laboratory Techniques inBiochemistry and Molecular Biology-Hybridization with Nucleic AcidProbes, (Elsevier, N.Y.).

As used herein, a “genomic region” is a segment of a chromosome in thegenome of a cell that is present on either side of the target site or,alternatively, also comprises a portion of the target site. The genomicregion can comprise at least 5-10, 5-15, 5-20, 5-25, 5-30, 5-35, 5-40,5-45, 5-50, 5-55, 5-60, 5-65, 5-70, 5-75, 5-80, 5-85, 5-90, 5-95, 5-100,5-200, 5-300, 5-400, 5-500, 5-600, 5-700, 5-800, 5-900, 5-1000, 5-1100,5-1200, 5-1300, 5-1400, 5-1500, 5-1600, 5-1700, 5-1800, 5-1900, 5-2000,5-2100, 5-2200, 5-2300, 5-2400, 5-2500, 5-2600, 5-2700, 5-2800. 5-2900,5-3000, 5-3100 or more bases such that the genomic region has sufficienthomology to undergo homologous recombination with the correspondingregion of homology.

Polynucleotides of interest and/or traits can be stacked together in acomplex trait locus as described in US 2013/0263324-A1, published Oct.3, 2013 and in PCT/U.S. Ser. No. 13/22,891, published Jan. 24, 2013,both applications are hereby incorporated by reference. The guidepolynucleotide/Cas9 endonuclease system described herein provides for anefficient system to generate double strand breaks and allows for traitsto be stacked in a complex trait locus.

The structural similarity between a given genomic region and thecorresponding region of homology found on the donor DNA can be anydegree of sequence identity that allows for homologous recombination tooccur. For example, the amount of homology or sequence identity sharedby the “region of homology” of the donor DNA and the “genomic region” ofthe organism genome can be at least 50%, 55%, 60%, 65%, 70%, 75%, 80%,81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%,95%, 96%, 97%, 98%, 99% or 100% sequence identity, such that thesequences undergo homologous recombination

The region of homology on the donor DNA can have homology to anysequence flanking the target site. While in some embodiments the regionsof homology share significant sequence homology to the genomic sequenceimmediately flanking the target site, it is recognized that the regionsof homology can be designed to have sufficient homology to regions thatmay be further 5′ or 3′ to the target site. In still other embodiments,the regions of homology can also have homology with a fragment of thetarget site along with downstream genomic regions. In one embodiment,the first region of homology further comprises a first fragment of thetarget site and the second region of homology comprises a secondfragment of the target site, wherein the first and second fragments aredissimilar.

As used herein, “homologous recombination” includes the exchange of DNAfragments between two DNA molecules at the sites of homology. Thefrequency of homologous recombination is influenced by a number offactors. Different organisms vary with respect to the amount ofhomologous recombination and the relative proportion of homologous tonon-homologous recombination. Generally, the length of the region ofhomology affects the frequency of homologous recombination events: thelonger the region of homology, the greater the frequency. The length ofthe homology region needed to observe homologous recombination is alsospecies-variable. In many cases, at least 5 kb of homology has beenutilized, but homologous recombination has been observed with as littleas 25-50 bp of homology. See, for example, Singer et al. 1982. Cell31:25-33; Shen and Huang. 1986. Genetics 112:441-57; Watt et al. 1985.Proc. Natl. Acad. Sci. USA 82:4768-72, Sugawara and Haber. 1992. MolCell Biol 12:563-75, Rubnitz and Subramani. (1984. Mol Cell Biol4:2253-8; Ayares et al. 1986. Proc. Natl. Acad. Sci. USA 83:5199-203;Liskay et al. 1987. Genetics 115:161-7.

Homology-directed repair (HDR) is a mechanism in cells to repairdouble-stranded and single stranded DNA breaks. Homology-directed repairincludes homologous recombination (HR) and single-strand annealing (SSA)(Lieber. 2010 Annu. Rev. Biochem. 79:181-211). The most common form ofHDR is called homologous recombination (HR), which has the longestsequence homology requirements between the donor and acceptor DNA. Otherforms of HDR include single-stranded annealing (SSA) andbreakage-induced replication, and these require shorter sequencehomology relative to HR. Homology-directed repair at nicks(single-stranded breaks) can occur via a mechanism distinct from HDR atdouble-strand breaks (Davis and Maizels 2014. PNAS (0027-8424), 111(10), p. E924-E932).

Alteration of the genome of a plant cell, for example, throughhomologous recombination (HR), is a powerful tool for geneticengineering. Homologous recombination has been demonstrated in plants(Halfter et al. 1992. Mol Gen Genet 231:186-93) and insects (Dray andGloor. 1997. Genetics 147:689-99). Homologous recombination has alsobeen accomplished in other organisms. For example, at least 150-200 bpof homology was required for homologous recombination in the parasiticprotozoan Leishmania (Papadopoulou and Dumas. 1997. Nucleic Acids Res25:4278-86). In the filamentous fungusAspergillus nidulans, genereplacement has been accomplished with as little as 50 bp flankinghomology (Chaveroche et al. 2000. Nucleic Acids Res 28:e97). Targetedgene replacement has also been demonstrated in the ciliate Tetrahymenathermophila (Gaertig et al. 1994. Nucleic Acids Res 22:5391-8). Inmammals, homologous recombination has been most successful in the mouseusing pluripotent embryonic stem cell lines (ES) that can be grown inculture, transformed, selected and introduced into a mouse embryo(Watson et al., 1992, Recombinant DNA, 2nd Ed., (Scientific AmericanBooks distributed by WH Freeman & Co.).

Error-prone DNA repair mechanisms can produce mutations at double-strandbreak sites. The Non-Homologous-End-Joining (NHEJ) pathways are the mostcommon repair mechanism to bring the broken ends together (Bleuyard etal. 2006. DNA Repair 5:1-12). The structural integrity of chromosomes istypically preserved by the repair, but deletions, insertions, or otherrearrangements are possible. The two ends of one double-strand break arethe most prevalent substrates of NHEJ (Kirik et al. 2000. EMBO J19:5562-6), however if two different double-strand breaks occur, thefree ends from different breaks can be ligated and result in chromosomaldeletions (Siebert and Puchta. 2002. Plant Cell 14:1121-31), orchromosomal translocations between different chromosomes (Pacher et al.2007. Genetics 175:21-9).

Episomal DNA molecules can also be ligated into the double-strand break,for example, integration of T-DNAs into chromosomal double-strand breaks(Chilton and Que. 2003. Plant Physiol 133:956-65; Salomon and Puchta.1998. EMBO J 17:6086-95). Once the sequence around the double-strandbreaks is altered, for example, by exonuclease activities involved inthe maturation of double-strand breaks, gene conversion pathways canrestore the original structure if a homologous sequence is available,such as a homologous chromosome in non-dividing somatic cells, or asister chromatid after DNA replication (Molinier et al. 2004. Plant Cell16:342-52). Ectopic and/or epigenic DNA sequences may also serve as aDNA repair template for homologous recombination (Puchta. 1999. Genetics152:1173-81).

Once a double-strand break is induced in the DNA, the cell's DNA repairmechanism is activated to repair the break. Error-prone DNA repairmechanisms can produce mutations at double-strand break sites. The mostcommon repair mechanism to bring the broken ends together is thenonhomologous end-joining (NHEJ) pathway (Bleuyard et al., (2006) DNARepair 5:1-12). The structural integrity of chromosomes is typicallypreserved by the repair, but deletions, insertions, or otherrearrangements are possible (Siebert and Puchta. 2002. Plant Cell14:1121-31; Pacher et al. 2007. Genetics 175:21-9).

Alternatively, the double-strand break can be repaired by homologousrecombination between homologous DNA sequences. Once the sequence aroundthe double-strand break is altered, for example, by exonucleaseactivities involved in the maturation of double-strand breaks, geneconversion pathways can restore the original structure if a homologoussequence is available, such as a homologous chromosome in non-dividingsomatic cells, or a sister chromatid after DNA replication (Molinier etal., (2004) Plant Cell 16:342-52). Ectopic and/or epigenic DNA sequencesmay also serve as a DNA repair template for homologous recombination(Puchta, (1999) Genetics 152:1173-81).

DNA double-strand breaks appear to be an effective factor to stimulatehomologous recombination pathways (Puchta et al., (1995) Plant Mol Biol28:281-92; Tzfira and White, (2005) Trends Biotechnol 23:567-9; Puchta,(2005) J Exp Bot 56:1-14). Using DNA-breaking agents, a two- tonine-fold increase of homologous recombination was observed betweenartificially constructed homologous DNA repeats in plants (Puchta etal., (1995) Plant Mol Biol 28:281-92). In maize protoplasts, experimentswith linear DNA molecules demonstrated enhanced homologous recombinationbetween plasmids (Lyznik et al., (1991) Mol Gen Genet 230:209-18).

The donor DNA may be introduced by any means known in the art. The donorDNA may be provided by any transformation method known in the artincluding, for example, Agrobacterium-mediated transformation orbiolistic particle bombardment. The donor DNA may be present transientlyin the cell or it could be introduced via a viral replicon. In thepresence of the Cas endonuclease and the target site, the donor DNA isinserted into the transformed plant's genome. (see guide language)

Further uses for guide RNA/Cas endonuclease systems have been described(See U.S. Patent Application US 2015-0082478 A1, published on Mar. 19,2015, WO2015/026886 A1, published on Feb. 26, 2015, US 2015-0059010 A1,published on Feb. 26, 2015, U.S. application 62/023,246, filed on Jul.07, 2014, and U.S. application 62/036,652, filed on Aug. 13, 2014, allof which are incorporated by reference herein) and include but are notlimited to modifying or replacing nucleotide sequences of interest (suchas a regulatory elements), insertion of polynucleotides of interest,gene knock-out, gene-knock in, modification of splicing sites and/orintroducing alternate splicing sites, modifications of nucleotidesequences encoding a protein of interest, amino acid and/or proteinfusions, and gene silencing by expressing an inverted repeat into a geneof interest. Knocking out the Wx1 gene

Methods for producing Waxy maize plants are provided herein and includeobtaining a plant or a seed thereof, wherein the plant or the seedcomprises a nucleic acid alteraction in a Wx1 gene that knocks outexpression of the gene, the nucleic acid alteration of which isgenerated by the introduction of one or more double strand breaks usinga double strand break inducing agent, and wherein the plant exhibits theWaxy maize phenotype, or grain with an increased percentage ofamylopectin compared to a maize plant comprising a functional Wx1 gene.

The double strand breaks are introduced into one or more target sites inan endogenous WX1 encoding sequence in a maize plant cell to produce amaize plant cell with a modified Wx1 nucleotide sequence that includes anucleic acid alteration that knocks out Wx1 gene function. The doublestrand break may be induced by a TALEN, a meganuclease, a zinc fingernuclease, a CRISPR-associated nuclease, or any other double strandinducing agent known to one of ordinary skill in the art.

The method may further include introducing a Wx1 polynucleotidemodification template in the maize plant cell, in which the Wx1polynucleotide modification template has at least one nucleic acidalteration (when compared to the endogenous WX1 encoding sequence) thatknocks out Wx1 gene function when incorporated into the endogenous WX1encoding sequence.

In one aspect, the CRISPR/CAS system is used to make double strandbreaks at target sites in and around the maize Wx1 gene, and the cell'sown repair mechanism joins the ends together. A target site may be anynucleotide sequence in the region of the Wx1 gene (or the endogenous WX1encoding sequence) that can be targeted for deletion using CRISPR/Casgene editing technology to generate a loss of function of the Wx1 gene.One or two guide RNAs may be used. If two guide RNAs are used, theintervening sequence is deleted as the gap is repaired by end joining.

A guide RNA may comprise a variable targeting domain that iscomplementary to SEQ ID NO:1 [WX-TS4], SEQ ID NO:2 [WX-TS8], SEQ ID NO:3[WX-TS10], SEQ ID NO:4 [WX-TS1], SEQ ID NO: 5 [WX-TS3], SEQ ID NO:6[WX-TS2], SEQ ID NO:7 [WX-TS6], SEQ ID NO:8 [WX-TS5], or SEQ ID NO:9[WX-TS7].

Multiple examples of deletions in the Wx1 nucleotide sequence that canbe produced via the CRISPR/Cas endonuclease system have been providedherein. The examples include: (1) deletion of whole coding sequencesincluding transcription start sites; (2) deletion of promoter region andcoding sequences; and (3) generation of frame shifts such as but notlimited to a frame shift with a small deletion or extended sequencedeletion at the exon 7/intron junction. However, the CRISPR-Casendonuclease system can be used to introduce any deletion that resultsin the loss of Waxy gene function.

CRISPR-Cas gene editing technology allows mutations in the Waxy gene tobe directly introduced into higher yielding elite inbreds in order tocreate commercial hybrids in the next immediate step. The inbred may befrom the Iowa Stiff Stalk Synthetic heterotic group, the non-Stiff Stalkheterotic group, or any other heterotic group known to one of ordinaryskill in the art.

A “heterotic group” comprises a set of genotypes that perform well whencrossed with genotypes from a different heterotic group (Hallauer et al.(1998) Corn breeding, p. 463-564. In G. F. Sprague and J. W. Dudley(ed.) Corn and corn improvement). Inbred lines are classified intoheterotic groups, and are further subdivided into families within aheterotic group, based on several criteria such as pedigree, molecularmarker-based associations, and performance in hybrid combinations (Smithet al. (1990) Theor. Appl. Gen. 80:833-840). The two most widely usedheterotic groups in the United States are referred to as “Iowa StiffStalk Synthetic” (also referred to herein as “stiff stalk”) and“Lancaster” or “Lancaster Sure Crop” (sometimes referred to as NSS, ornon-Stiff Stalk).

Some heterotic groups possess the traits needed to be a female parent,and others, traits for a male parent. For example, in maize, yieldresults from public inbreds released from a population called BSSS (IowaStiff Stalk Synthetic population) has resulted in these inbreds andtheir derivatives becoming the female pool in the central Cornbelt. BSSSinbreds have been crossed with other inbreds, e.g. SD 105 and MaizAmargo, and this general group of materials has become known as StiffStalk Synthetics (SSS) even though not all of the inbreds are derivedfrom the original BSSS population (Mikel and Dudley (2006) Crop Sci:46:1193-1205). By default, all other inbreds that combine well with theSSS inbreds have been assigned to the male pool, which for lack of abetter name has been designated as NSS, i.e. Non-Stiff Stalk. This groupincludes several major heterotic groups such as Lancaster Surecrop,Iodent, and Leaming Corn.

Maize hybrids may be created by crossing an Iowa Stiff Stalk Syntheticinbred plant with a non-Stiff Stalk inbred plant. Mutations that resultin a loss of function of the Wx1 gene are recessive; hence, a loss offunction allele (whether the same or different) must be present in eachof the inbred parents to generate a hybrid maize plant with the Waxyphenotype. Introducing a loss of function allele into each inbred parenteliminates the need for multiple cycles of breeding to produce a Waxymaize commercial product. Moreover, the methods described herein breakthe linkage with genetic material that has a negative impact on theplant, such as for example, on yield. Hence, when a Waxy maize hybridplant produced by crossing a male inbred with a female inbred, whereinboth comprise a loss of function allele of the Wx1 gene, is compared toa wild-type maize plant produced by genetically similar inbred parents,except the parents do not have loss of function alleles at the Wx1 gene,no significant difference in yield should be observed.

Moreover, segregation as part of the breeding process eliminates allother foreign genetic elements, making the process akin to naturalmutagenesis.

“Maize” refers to a plant of the Zea mays L. ssp. mays and is also knownas “corn”. These terms are used interchangeably herein.

EXAMPLES

In the following Examples, unless otherwise stated, in which parts andpercentages are by weight and degrees are Celsius. It should beunderstood that these Examples, while indicating embodiments of theinvention, are given by way of illustration only. From the abovediscussion and these Examples, one skilled in the art, can make variouschanges and modifications of the invention to adapt it to various usagesand conditions. Such modifications are also intended to fall within thescope of the appended embodiments.

EXAMPLE 1 Knocking out the Wx1 Gene in Maize Elite Lines: Target SiteSelection and Cas9 and Guide RNA Vector Construction Target SiteSelection

The gRNA/Cas9 Site directed nuclease system, described in WO2015026885,WO20158026887, WO2015026883, and WO2015026886, was used to knock out theWaxy gene in maize. The following pairs of target sites were used fordeletion of the entire Waxy coding sequence: WX-TS4 with WX-TS8; WX-TS4with WX-TS7; WX-TS4 with WX-TS5; WX-TS6 with WX-TS8; WX-TS6 with WX-TS7;and WX-TS6 with WX-TS5. The paired target sites WX-TS10 and WX-TS8 wereused for promoter and coding sequence deletion, and WX-TS1 was usedalone or paired with WX-TS3 or WX-TS2 for frame shift deletions in theexon 7 and subsequent intron region. Most target site sequences wereconserved in all the inbred lines used except WX-TS7 which was onlypresent in one line. The location of each target site in the Waxygenomic sequence is shown in FIG. 1A, and the target sequences arelisted in Table 1. FIG. 1B also shows a schematic drawing of themutation types.

TABLE 1 Maize Wx1 genomic target site sequences Target Site Desig-Maize Genomic PAM SEQ ID nation Target Site Sequence Sequence NO: WX-TS4GCCCAAAACGCTTTCCCGAT CGG 1 WX-TS8 GCAATATAAAATTACCGAT CGG 2 WX-TS10GCTGGGAGAGACGGTGTAGTA GGG 3 WX-TS1 GGCATCTACAGGGACGCAA AGG 4 WX-TS3GAGCATGGAGAACGAAGA CGG 5 WX-TS2 GCTCGTATATACCTCGTC TGG 6 WX-TS6GCTGGTGCGCAGTGCCGG GGG 7 WX-TS5 GACAATGCCCTAAATATCTAT AGG 8 WX-TS7GAGACCATAGCCTATCTT TGG 9

Cas9 Vector Construction

The Cas9 gene from Streptococcus pyogenesM1 GAS (SF370) (SEQ ID NO:10)was maize codon optimized per standard techniques known in the art andthe potato ST-LS1 intron was introduced in order to eliminate itsexpression in E.coli and Agrobacterium. To facilitate nuclearlocalization of the Cas9 protein in maize cells, Simian virus 40 (SV40)monopartite amino terminal nuclear localization signal (MAPKKKRKVH, SEQID NO:11) was incorporated at the amino terminus of the Cas9 openreading frame. The maize optimized Cas9 gene was operably linked to amaize Ubiquitin promoter using standard molecular biological techniques.

Guide RNA Vector Construction

To direct Cas9 nuclease to the designated genomic target sites (Table1), a maize U6 polymerase III promoter (SEQ ID NO:12; see WO02015026885,WO20158026887, WO02015026883, and WO2015026886) and its cognate U6polymerase III termination sequences (TTTTTTTT) were used to directinitiation and termination of gRNA expression. Guide RNA variabletargeting domains for Waxy gene mutagenesis are identified as WXY-CR1,WXY-CR2, WXY-CR3, WXY-CR4, WXY-CR5, WXY-CR6, WXY-CR7, WXY-CR8, andWXY-CR10, which correspond to the genomic target sites WX-TS1, WX-TS2,WX-TS3, WX-TS4, WX-TS5, WX-TS6, WX-TS7, WX-TS8, and WX-TS10,respectively. DNA encoding each of the variable nucleotide targetingdomains was cloned into a gRNA expression cassette through Bsbl sitesusing double strand oligos. Each guide RNA expression cassette (Table 2)thus consists of the U6 polymerase III maize promoter operably linked tothe DNA version of the guide RNA, which consists of the respectivenucleotide variable targeting domain followed by a polynucleotidesequence capable of interacting with the double strand break inducingendonuclease, and then the cognate U6 polymerase III terminationsequence.

TABLE 2 Guide RNA Expression Cassettes Guide RNA expression DNA versionof cassette guide RNA Name SEQ ID NO: SEQ ID NO: WXY-CR4 13 22 WXY-CR814 23 WXY-CR10 15 24 WXY-CR1 16 25 WXY-CR3 17 26 WXY-CR2 18 27 WXY-CR619 28 WXY-CR7 20 29 WXY-CR5 21 30

EXAMPLE 2 Delivery of the Guide RNA/Cas9 Endonuclease System DNA toMaize

Plasmids containing the Cas9 and guide RNA expression cassettesdescribed above were co-bombarded with plasm ids containing thetransformation selectable marker NPTII and the transformation enhancingdevelopmental genes ODP2 (AP2 domain transcription factor ODP2 (Ovuledevelopment protein 2)) and Wuschel into elite maize lines' genomes.Transformation of maize immature embryos can be performed using anymethod known in the art or the method described below.

In one transformation method, ears are husked and surface sterilized in30-50% Clorox bleach plus 0.5% Micro detergent for 10 minutes and thenrinsed two times with sterile water. The immature embryos are isolatedand placed embryo axis side down (scutellum side up), with 25 embryosper plate, on 13224E medium for 2-4 hours and then aligned within the2.5-cm target zone in preparation for bombardment.

DNA of plasmids is adhered to 0.6 μm (average diameter) gold pelletsusing a proprietary lipid-polymer mixture of TransIT®-2020 (Cat# MIR5404, Mirus Bio LLC, Madison, Wis. 5371). DNA solution was preparedusing 1 μg of plasmid DNA and optionally, other constructs were preparedfor co-bombardment using 10 ng (0.5 μl) of each plasmid. To thepre-mixed DNA, 50 μl of prepared gold particles (30 mg/ml) and 1 μlTransIT®-2020 are added and mixed carefully. The final mixture isallowed to incubate under constant vortexing at low speed for 10minutes. After the precipitation period, the tubes are centrifugedbriefly, and liquid is removed. Gold particles are pelleted in amicrofuge at 10,000 rpm for 1 min, and aqueous supernatant is removed.120 μl of 100% EtOH is added, and the particles are resuspended by briefsonication. Then, 10 μl is spotted on to the center of each macrocarrierand allowed to dry about 2 minutes before bombardment, with a total often aliquots taken from each tube of prepared particles/DNA.

The sample plates are bombarded with a Biolistic PDA-1000/He (Bio-Rad).Embryos are 6 cm from the macrocarrier, with a gap of 1/8^(th) of aninch between the 200 psi rupture disc and the macrocarrier. All samplesreceive a single shot.

Following bombardment, the embryos are incubated on the bombardmentplate for ˜20 hours then transferred to 13266L (rest/induction medium)for 7-9 days at temperatures ranging from 26-30° C. Embryos are thentransferred to the maturation media 289H for ˜21 days. Mature somaticembryos are then transferred to germination media 272G and moved to thelight. In about 1 to 2 weeks plantlets containing viable shoots androots are sampled for analysis and sent to the greenhouse where they aretransferred to flats (equivalent to a 2.5″ pot) containing potting soil.After 1-2 weeks, the plants are transferred to Classic 600 pots (1.6gallon) and grown to maturity.

Media:

Bombardment medium (13224E) comprises 4.0 g/I N6 basal salts (SIGMAC-1416), 1.0 ml/l Eriksson's Vitamin Mix (1000× SIGMA-1511), 0.5 mg/lthiamine HCl, 190.0 g/l sucrose, 1.0 mg/l 2,4-D, and 2.88 g/l L-proline(brought to volume with D-I H2O following adjustment to pH 5.8 withKOH); 6.3 g/l Sigma agar (added after bringing to volume with D-I H2O);and 8.5 mg/l silver nitrate (added after sterilizing the medium andcooling to room temperature).

Selection medium (13266L) comprises 1650 mg/l ammonium Nitrate, 277.8mg/l ammonium Sulfate, 5278 mg/l potassium nitrate, calcium chloride,anhydrous 407.4 mg/l calcium chloride, anhydrous, 234.92 mg/l magnesiumsulfate, anhydrous, 410 mg/l potassium phosphate, monobasic, 8 mg/lboric acid, 8.6 mg/l, zinc sulfate.7h2o, 1.28 mg/l potassium iodide,44.54 mg/l ferrous sulfate.7h2o, 59.46 mg/l na2edta.2h2o, 0.025 mg/lcobalt chloride.6h2o, 0.4 mg/l molybdic acid (sodium salt).2h2o, 0.025mg/l cupric sulfate.5h2o, 6 mg/l manganese sulfate monohydrate, 2 mg/lthiamine, 0.6 ml/l b5h minor salts 1000×, 0.4 ml/l eriksson's vitamins1000×, 6 ml/l s&h vitamin stock 100×, 1.98 g/l l-proline, 3.4 mg/lsilver nitrate, 0.3 g/l casein hydrolysate (acid), 20 g/l sucrose, 0.6g/l glucose, 0.8 mg/l2,4-d, 1.2 mg/l dicamba, 6 g/l tc agar, 100 mg/lagribio carbenicillin, 25 mg/l cefotaxime, and 150 mg/l geneticin (g418)

Plant regeneration medium (289H) comprises 4.3 g/l MS salts (GIBCO11117-074), 5.0 ml/l MS vitamins stock solution (0.100 g nicotinic acid,0.02 g/l thiamine HCL, 0.10 g/l pyridoxine HCL, and 0.40 g/l glycinebrought to volume with polished D-I H2O) (Murashige and Skoog (1962)Physiol. Plant. 15:473), 100 mg/l myo-inositol, 0.5 mg/l zeatin, 60 g/lsucrose, and 1.0 ml/l of 0.1 mM abscisic acid (brought to volume withpolished D-I H2O after adjusting to pH 5.6); 8.0 g/l Sigma agar (addedafter bringing to volume with D-I H2O); and 1.0 mg/l indoleacetic acidand 150 mg/l Geneticin (G418) (added after sterilizing the medium andcooling to 60° C.).

Hormone-free medium (272G) comprises 4.3 g/l MS salts (GIBCO 11117-074),5.0 ml/l MS vitamins stock solution (0.100 g/l nicotinic acid, 0.02 g/lthiamine HCL, 0.10 g/l pyridoxine HCL, and 0.40 g/l glycine brought tovolume with polished D-I H2O), 0.1 g/l myo-inositol, and 40.0 g/lsucrose (brought to volume with polished D-I H2O after adjusting pH to5.6); and 0.5 mg/l IBA and 150 mg/l Geneticin (G418) and 6 g/lbacto-agar (added after bringing to volume with polished D-I H2O),sterilized and cooled to 60° C.

EXAMPLE 3 Screening of T0 Plants and Event Characterization

To identify whole Wx1 gene deletion positive events, genomic DNA wasextracted from leaf tissue of T0 plants, and qPCR was performed usingQuantiTect Mulitplex qPCR Kit (QIAGEN, CAT no. 204545) and the primerslisted in Table 3. Primer locations are shown in FIG. 2A. Ampliconsobtained when the CR4/CR8, CR4/CR5, CR4/CR7, CR6/CR8, CR6/CR5, CR6/CR7or CR10/CR8 were cleaved and ligated together after the sequence (3.8 kb-6.2 kb) between the two sites was deleted were removed from thescreening process. As an example, FIG. 3 shows a sequence alignment ofgenerated mutations at the CR4/CR8 deletion junction; and FIG. 4 shows asequence alignment of generated mutations at the CR10/CR8 junction.FIGS. 3 and 4 show a small sample of the generated mutations that wereobtained.

Next Generation Sequencing (NGS) was used to evaluate the junctionsequences in the deletion qPCR positive events. The junction was PCRamplified with PHUSION® Flash High Fidelity PCR Master Mix (New EnglandBiolabs, F-548). The primers used in the primary PCR reaction are shownin Table 4 and the primers used in the secondary PCR reaction are:

(forward, SEQ ID NO: 38)AATGATACGGCGACCACCGAGATCTACACATACGAGATCCGTAatcggga agctgaag and(reverse, SEQ ID NO: 39)CAAGCAGAAGACGGCATACGAGATNNNNNNNNACACGCACGatccgacgg tagtgt.

NNNNNNNN are the barcode sequences corresponding to sample locations ona plate.

TABLE 3 Primers used to screen for Wx1 whole gene deletions Name ofPrimer Primer SEQ deletion name Orientation Primary PCR Primer SequenceID NO: CR4(CR6)/CR8 P4F Forward GTGTGCGTGCGTGCAGAC 31 (CR7 or P8RReverse AGCAGGGATTATTTACTCCACCAC 32 CR5) P7R Reverse GCCAGAAGCTGCCAGAAGC33 P5R Reverse GCTAAATGTAGGTGAATGAAACAAGAA 34 CR10-CR8 CR4 probeCAAGCCAAGGCGAGG 35 P10F Forward CATATGGAGAGGTTAAGACAGCAATT 36 P8RReverse AGCAGGGATTATTTACTCCACCAC 32 CR10 probe AATTTGATGCCGTCCTAT 37

TABLE 4 NGS first PCR primers Primer SEQ ID Name OrientationPrimary PCR Primer Sequence NO: CR4/CR6 ForwardatcgggaagctgaagTGCGTGCGTGCAGACGACAA 40 mipf1 CR8 mipr ReverseatccgacggtagtgtGAGGAGCGATAAGAACACCGAACA 41 CR5 mipr ReverseatccgacggtagtgtAAATGTAGGTGAATSAAACAAGAAAC 42 CR7 mipr ReverseatccgacggtagtgtGGATCTAGAAAGTGACAGATTCCTAATATTACA 43 CR10 mipf ForwardatcgggaagctgaagGGTTAAGACAGCAATTAATTTGATGCC 44 CR1 mipf ForwardatcgggaagctgaagGCCCTCTCTCGTGCTACCTCA 45 CR1 mipr ReverseatccgacggtagtgtGAAGATGGTCAGACAGACATGCAGT 46 Note: CR4/CR6mipf1 willcombine with reverse primers CR8, CR5, and CR7; CR10 mipf also combinedwith CR8 reverse primer.

Events containing a frameshift in Wx1 at exon 7, generated using guideRNA CR1, CR1/CR3, or CR1/CR2, were evaluated by NGS only due to a highmutation frequency (˜80%). T0 plants were selected based on sequenceanalysis (FIG. 5 shows a representation of deletions in the WX-TS1region). The pairings of CR4/CR5, CR4/CR7, CR6/CR8, CR6/CR7, and CR6/CR5generated deletions in Waxy in two transformed inbred lines. The CR4/CR8and CR10/CR8 were used in more inbreds, and deletion events wereobtained in most of them. A range of deletions (nucleotide insertions)were observed at the CR1 site. Moreover, a WX-D7□30 bp mutant whichmimicked the natural mutant (China waxy) was generated in 2 inbred lineswhen CR1/CR3 guide RNAs were used.

T1 Analysis

T0 plants harboring the created wx1 alleles were transferred to acontrolled environment. Pollen from (Wx1/wx1) T0 plants was carried torecurrent parent plants to produce seed. Some pollen from the T0 plantswas stained with potassium iodide solution (Lugol, Sigma 62650). FIG. 6Ashows wild-type Wx1 pollen (darker stained) compared to the generatedmutant wx1 pollen (lighter stained).

T1 plants went through more comprehensive molecular characterization tonot only confirm that mutations observed in T0 plant were stablyinherited but also to verify that the T1 or later generation plants werefree from any foreign DNA elements used during the transformationprocess. First, qPCR was performed on all helper genes including Cas9,the guide RNAs, the transformation selection marker (NPTII), and thetransformation enhancing genes ODP2 and WUS2 to make sure the genessegregated away from the generated wx1 mutant alleles. Then the T1plants were sampled using Southern by Sequencing (SbS) analysis tofurther demonstrate that the plants are free of any foreign DNA(Zastron-Hayes et al. 2015. The Plant Genome 8.doi:10.3835/plantgenome2014.08.0037).

BC₀F₂ (selfed T1) seeds showed segregating Waxy maize kernels (FIG. 6B)amongst normal kernels on an ear. A 3 normal kernel:1 Waxy kernelsegregation pattern was observed.

In flours ground from separated BC₁F₂ segregating material (T3 seed), aMegazyme kit was used to determine amylose vs. amylopectin ratios (Table5). The results showed no significant differences in Waxy amylopectin %between example inbreds generated using CRISPR/CAS system(EMTA.2015.G091.2.5 & EMTA.2015.G093.1.6), compared to its equivalentinbreds generated by conventional introgression breeding (PH184CWX1Check1 and Check2). The Megazyme kit is the industry standard foramylose/amylopectin determinations in cereal flours, based on the methoddescribed in Yun, S. H. and Matheson, N. K. 1990. Starch/Starke42:302-305. Similar confirmations of amylose/amylopectin determinationscan be conducted on additional inbred or hybrid material.

What is claimed is:
 1. A method for obtaining a Waxy maize plant, themethod comprising: a) introducing a double-strand break at at least onetarget site in an endogenous WX1 encoding sequence in a maize plant cellto produce a maize plant cell with a modified Wx1 nucleotide sequence,wherein the modified Wx1 nucleotide sequence comprises a nucleic acidalteration that knocks out Wx1 gene function; and b) generating a maizeplant from the maize plant cell of (a), wherein said maize plantproduces grain with an increased percentage of amylopectin compared to asecond maize plant comprising a functional Wx1 gene.
 2. The method ofclaim 1, further comprising introducing a Wx1 polynucleotidemodification template in the maize plant cell, wherein said Wx1polynucleotide modification template comprises at least one nucleic acidalteration that knocks out Wx1 gene function and said Wx1 polynucleotidemodification template is incorporated into the endogenous WX1 encodingsequence.
 3. The method of claim 1, wherein said double-strand break isinduced by a nuclease selected from the group consisting of: a TALEN, ameganuclease, a zinc finger nuclease, and a CRISPR-associated nuclease.4. The method of claim 1, wherein said double-strand break is induced bya CRISPR-associated nuclease and wherein a guide RNA is provided.
 5. Themethod of claim 4, wherein said guide RNA comprises a variable targetingdomain that is complementary to SEQ ID NO:4 [WX-TS1].
 6. The method ofclaim 1, wherein said double-stranded break is induced by aCRISPR-associated nuclease and wherein a pair of guide RNAs areprovided.
 7. The method of claim 6, wherein said pair of guide RNAscomprises: a. a first guide RNA comprising a variable targeting domainthat is complementary to SEQ ID NO:1 [WX-TS4] and a second guide RNAcomprising a variable targeting domain that is complementary to SEQ IDNO:2 [WX-TS8]; b. a first guide RNA comprising a variable targetingdomain that is complementary to SEQ ID NO:1 [WX-TS4] and a second guideRNA comprising a variable targeting domain that is complementary to SEQID NO:9 [WX-TS7] c. a first guide RNA comprising a variable targetingdomain that is complementary to SEQ ID NO:1 [WX-TS4] and a second guideRNA comprising a variable targeting domain that is complementary to SEQID NO:8 [WX-TS5]; d. a first guide RNA comprising a variable targetingdomain that is complementary to SEQ ID NO:7 [WX-TS6] and a second guideRNA comprising a variable targeting domain that is complementary to SEQID NO:2 [WX-TS8]; e. a first guide RNA comprising a variable targetingdomain that is complementary to SEQ ID NO:7 [WX-TS6] and a second guideRNA comprising a variable targeting domain that is complementary to SEQID NO:9 [WX-TS7]; f a first guide RNA comprising a variable targetingdomain that is complementary to SEQ ID NO:7 [WX-TS6] and a second guideRNA comprising a variable targeting domain that is complementary to SEQID NO:8 [WX-TS5]; g. a first guide RNA comprising a variable targetingdomain that is complementary to SEQ ID NO:3 [WX-TS10] and a second guideRNA comprising a variable targeting domain that is complementary to SEQID NO:2 [WX-TS8]; h. a first guide RNA comprising a variable targetingdomain that is complementary to SEQ ID NO:4 [WX-TS1] and a second guideRNA comprising a variable targeting domain that is complementary to SEQID NO: 5 [WX-TS3]; or i. a first guide RNA comprising a variabletargeting domain that is complementary to SEQ ID NO:4 [WX-TS1] and asecond guide RNA comprising a variable targeting domain that iscomplementary to SEQ ID NO:6 [WX-TS2].
 8. The method of claim 1, whereinsaid Cas endonuclease is a Cas9 endonuclease.
 9. The method of claim 1,wherein a gene encoding the Cas endonuclease is optimized for maize. 10.The method of claim 1, wherein a gene encoding the Cas endonuclease isoperably linked to an SV40 nuclear targeting signal upstream of the Cascoding region.
 11. The method of claim 1, wherein the nucleic acidalteration occurs in an elite inbred maize plant.
 12. A plant producedby the method of claim
 1. 13. Seed produced by the plant of claim 12.14. A guide polynucleotide comprising a variable targeting domain thatis complementary to a target site in an endogenous WX1 encoding sequencein a maize plant cell.
 15. The guide polynucleotide of claim 14, whereinsaid guide polynucleotide comprises an RNA sequence, a DNA sequence, oran RNA-DNA combination sequence.
 16. The guide polynucleotide of claim14, wherein said variable targeting domain is complementary to a memberof the group consisting of: a) SEQ ID NO:1; b) SEQ ID NO:2; c) SEQ IDNO:3; d) SEQ ID NO:4; e) SEQ ID NO:5; f) SEQ ID NO:6; g) SEQ ID NO:7; h)SEQ ID NO:8; and i) SEQ ID NO:9.
 17. A method of producing a Waxy maizehybrid plant, said method comprising crossing an Iowa Stiff StalkSynthetic maize inbred plant comprising a nucleic acid alteration thatknocks out Wx1 gene function, with a non-Stiff Stalk maize inbred plantcomprising a nucleic acid alteration that knocks out Wx1 gene function.